diff --git a/maternal-app/maternal-app-backend/src/modules/analytics/analytics.controller.ts b/maternal-app/maternal-app-backend/src/modules/analytics/analytics.controller.ts
index b80ca44..51776b5 100644
--- a/maternal-app/maternal-app-backend/src/modules/analytics/analytics.controller.ts
+++ b/maternal-app/maternal-app-backend/src/modules/analytics/analytics.controller.ts
@@ -6,11 +6,14 @@ import {
   Req,
   Res,
   Header,
+  BadRequestException,
 } from '@nestjs/common';
 import { Response } from 'express';
 import { PatternAnalysisService } from './pattern-analysis.service';
 import { PredictionService } from './prediction.service';
 import { ReportService } from './report.service';
+import { ComparisonService } from './comparison.service';
+import { ComparisonMetric } from './dto/comparison.dto';
 
 @Controller('api/v1/analytics')
 export class AnalyticsController {
@@ -18,6 +21,7 @@ export class AnalyticsController {
     private readonly patternAnalysisService: PatternAnalysisService,
     private readonly predictionService: PredictionService,
     private readonly reportService: ReportService,
+    private readonly comparisonService: ComparisonService,
   ) {}
 
   @Get('insights/:childId')
@@ -128,4 +132,69 @@ export class AnalyticsController {
       });
     }
   }
+
+  @Get('compare')
+  async compareChildren(
+    @Req() req: any,
+    @Query('childIds') childIdsParam: string,
+    @Query('metric') metricParam: string,
+    @Query('startDate') startDate: string,
+    @Query('endDate') endDate: string,
+  ) {
+    // Validate required parameters
+    if (!childIdsParam) {
+      throw new BadRequestException('childIds query parameter is required (comma-separated)');
+    }
+
+    if (!metricParam) {
+      throw new BadRequestException('metric query parameter is required');
+    }
+
+    if (!startDate || !endDate) {
+      throw new BadRequestException('startDate and endDate query parameters are required');
+    }
+
+    // Parse child IDs
+    const childIds = childIdsParam.split(',').filter(id => id.trim());
+
+    if (childIds.length < 2) {
+      throw new BadRequestException('At least 2 children are required for comparison');
+    }
+
+    // Validate metric
+    const validMetrics = Object.values(ComparisonMetric);
+    if (!validMetrics.includes(metricParam as ComparisonMetric)) {
+      throw new BadRequestException(
+        `Invalid metric. Must be one of: ${validMetrics.join(', ')}`,
+      );
+    }
+
+    const metric = metricParam as ComparisonMetric;
+
+    // Parse dates
+    const start = new Date(startDate);
+    const end = new Date(endDate);
+
+    if (isNaN(start.getTime()) || isNaN(end.getTime())) {
+      throw new BadRequestException('Invalid date format. Use ISO 8601 format (YYYY-MM-DD)');
+    }
+
+    if (start > end) {
+      throw new BadRequestException('startDate must be before endDate');
+    }
+
+    // Perform comparison
+    const comparison = await this.comparisonService.compareChildren(
+      req.user.userId,
+      childIds,
+      metric,
+      start,
+      end,
+    );
+
+    return {
+      success: true,
+      data: comparison,
+    };
+  }
 }
diff --git a/maternal-app/maternal-app-backend/src/modules/analytics/analytics.module.ts b/maternal-app/maternal-app-backend/src/modules/analytics/analytics.module.ts
index f040d70..d60a1fa 100644
--- a/maternal-app/maternal-app-backend/src/modules/analytics/analytics.module.ts
+++ b/maternal-app/maternal-app-backend/src/modules/analytics/analytics.module.ts
@@ -2,16 +2,18 @@ import { Module } from '@nestjs/common';
 import { TypeOrmModule } from '@nestjs/typeorm';
 import { Activity } from '../../database/entities/activity.entity';
 import { Child } from '../../database/entities/child.entity';
+import { FamilyMember } from '../../database/entities/family-member.entity';
 import { PatternAnalysisService } from './pattern-analysis.service';
 import { PredictionService } from './prediction.service';
 import { ReportService } from './report.service';
+import { ComparisonService } from './comparison.service';
 import { AnalyticsController } from './analytics.controller';
 import { InsightsController } from './insights.controller';
 
 @Module({
-  imports: [TypeOrmModule.forFeature([Activity, Child])],
+  imports: [TypeOrmModule.forFeature([Activity, Child, FamilyMember])],
   controllers: [AnalyticsController, InsightsController],
-  providers: [PatternAnalysisService, PredictionService, ReportService],
-  exports: [PatternAnalysisService, PredictionService, ReportService],
+  providers: [PatternAnalysisService, PredictionService, ReportService, ComparisonService],
+  exports: [PatternAnalysisService, PredictionService, ReportService, ComparisonService],
 })
 export class AnalyticsModule {}
diff --git a/maternal-app/maternal-app-backend/src/modules/analytics/comparison.service.ts b/maternal-app/maternal-app-backend/src/modules/analytics/comparison.service.ts
new file mode 100644
index 0000000..8095c27
--- /dev/null
+++ b/maternal-app/maternal-app-backend/src/modules/analytics/comparison.service.ts
@@ -0,0 +1,505 @@
+import { Injectable, ForbiddenException } from '@nestjs/common';
+import { InjectRepository } from '@nestjs/typeorm';
+import { Repository, Between } from 'typeorm';
+import { Activity, ActivityType } from '../../database/entities/activity.entity';
+import { Child } from '../../database/entities/child.entity';
+import { FamilyMember } from '../../database/entities/family-member.entity';
+import {
+  ComparisonMetric,
+  ComparisonResult,
+  ComparisonChildData,
+  SleepComparisonData,
+  FeedingComparisonData,
+  DiapeChangesComparisonData,
+  ActivitiesComparisonData,
+} from './dto/comparison.dto';
+import {
+  startOfDay,
+  endOfDay,
+  eachDayOfInterval,
+  differenceInMonths,
+  format,
+  isWithinInterval,
+  parseISO,
+} from 'date-fns';
+
+@Injectable()
+export class ComparisonService {
+  constructor(
+    @InjectRepository(Activity)
+    private activityRepository: Repository<Activity>,
+    @InjectRepository(Child)
+    private childRepository: Repository<Child>,
+    @InjectRepository(FamilyMember)
+    private familyMemberRepository: Repository<FamilyMember>,
+  ) {}
+
+  async compareChildren(
+    userId: string,
+    childIds: string[],
+    metric: ComparisonMetric,
+    startDate: Date,
+    endDate: Date,
+  ): Promise<ComparisonResult> {
+    // Validate at least 2 children
+    if (childIds.length < 2) {
+      throw new ForbiddenException('At least 2 children required for comparison');
+    }
+
+    // Verify all children exist and user has access
+    const children = await this.childRepository
+      .createQueryBuilder('child')
+      .where('child.id IN (:...childIds)', { childIds })
+      .andWhere('child.deletedAt IS NULL')
+      .getMany();
+
+    if (children.length !== childIds.length) {
+      throw new ForbiddenException('One or more children not found');
+    }
+
+    // Verify user has access to all children
+    const familyIds = [...new Set(children.map((c) => c.familyId))];
+    for (const familyId of familyIds) {
+      const membership = await this.familyMemberRepository.findOne({
+        where: { userId, familyId },
+      });
+
+      if (!membership) {
+        throw new ForbiddenException(
+          'You do not have access to one or more children',
+        );
+      }
+    }
+
+    // Route to appropriate comparison method
+    switch (metric) {
+      case ComparisonMetric.SLEEP_PATTERNS:
+        return this.compareSleepPatterns(children, startDate, endDate);
+      case ComparisonMetric.FEEDING_FREQUENCY:
+        return this.compareFeedingFrequency(children, startDate, endDate);
+      case ComparisonMetric.DIAPER_CHANGES:
+        return this.compareDiaperChanges(children, startDate, endDate);
+      case ComparisonMetric.ACTIVITIES:
+        return this.compareActivities(children, startDate, endDate);
+      default:
+        throw new ForbiddenException(`Unsupported metric: ${metric}`);
+    }
+  }
+
+  private async compareSleepPatterns(
+    children: Child[],
+    startDate: Date,
+    endDate: Date,
+  ): Promise<ComparisonResult> {
+    const childrenData: ComparisonChildData[] = [];
+
+    for (const child of children) {
+      const sleepActivities = await this.activityRepository.find({
+        where: {
+          childId: child.id,
+          type: ActivityType.SLEEP,
+          startedAt: Between(startOfDay(startDate), endOfDay(endDate)),
+        },
+        order: { startedAt: 'ASC' },
+      });
+
+      const data = this.calculateSleepData(sleepActivities, startDate, endDate);
+      const age = differenceInMonths(new Date(), new Date(child.birthDate));
+
+      childrenData.push({
+        childId: child.id,
+        childName: child.name,
+        age,
+        data,
+        summary: {
+          averageHoursPerDay: data.averageHoursPerDay,
+          totalSessions: data.totalSleepSessions,
+          nightSleepPercentage: data.nightSleepPercentage,
+        },
+      });
+    }
+
+    // Calculate overall summary
+    const overallSummary = {
+      averageHoursAcrossChildren:
+        childrenData.reduce((sum, c) => sum + c.data.averageHoursPerDay, 0) /
+        childrenData.length,
+      childWithMostSleep: childrenData.reduce((prev, current) =>
+        prev.data.averageHoursPerDay > current.data.averageHoursPerDay
+          ? prev
+          : current,
+      ).childName,
+      childWithLeastSleep: childrenData.reduce((prev, current) =>
+        prev.data.averageHoursPerDay < current.data.averageHoursPerDay
+          ? prev
+          : current,
+      ).childName,
+    };
+
+    return {
+      metric: ComparisonMetric.SLEEP_PATTERNS,
+      dateRange: { start: startDate, end: endDate },
+      children: childrenData,
+      overallSummary,
+    };
+  }
+
+  private calculateSleepData(
+    activities: Activity[],
+    startDate: Date,
+    endDate: Date,
+  ): SleepComparisonData {
+    const days = eachDayOfInterval({ start: startDate, end: endDate });
+    const totalDays = days.length;
+
+    let totalMinutes = 0;
+    let nightSleepMinutes = 0;
+    let longestSleepDuration = 0;
+
+    const dailyBreakdown = days.map((day) => {
+      const dayActivities = activities.filter((a) =>
+        isWithinInterval(new Date(a.startedAt), {
+          start: startOfDay(day),
+          end: endOfDay(day),
+        }),
+      );
+
+      let dayTotalMinutes = 0;
+      dayActivities.forEach((activity) => {
+        const start = new Date(activity.startedAt);
+        const end = activity.endedAt
+          ? new Date(activity.endedAt)
+          : new Date();
+        const duration = Math.floor((end.getTime() - start.getTime()) / 60000);
+
+        dayTotalMinutes += duration;
+        totalMinutes += duration;
+
+        if (duration > longestSleepDuration) {
+          longestSleepDuration = duration;
+        }
+
+        // Check if night sleep (8PM - 6AM)
+        const hour = start.getHours();
+        if (hour >= 20 || hour < 6) {
+          nightSleepMinutes += duration;
+        }
+      });
+
+      return {
+        date: format(day, 'yyyy-MM-dd'),
+        totalMinutes: dayTotalMinutes,
+        sessionsCount: dayActivities.length,
+      };
+    });
+
+    // Count naps (sleep sessions during 6AM - 8PM)
+    const naps = activities.filter((a) => {
+      const hour = new Date(a.startedAt).getHours();
+      return hour >= 6 && hour < 20;
+    });
+
+    return {
+      averageHoursPerDay: totalMinutes / totalDays / 60,
+      totalSleepSessions: activities.length,
+      longestSleepDuration,
+      averageNapsPerDay: naps.length / totalDays,
+      nightSleepPercentage:
+        totalMinutes > 0 ? (nightSleepMinutes / totalMinutes) * 100 : 0,
+      dailyBreakdown,
+    };
+  }
+
+  private async compareFeedingFrequency(
+    children: Child[],
+    startDate: Date,
+    endDate: Date,
+  ): Promise<ComparisonResult> {
+    const childrenData: ComparisonChildData[] = [];
+
+    for (const child of children) {
+      const feedingActivities = await this.activityRepository.find({
+        where: {
+          childId: child.id,
+          type: ActivityType.FEEDING,
+          startedAt: Between(startOfDay(startDate), endOfDay(endDate)),
+        },
+        order: { startedAt: 'ASC' },
+      });
+
+      const data = this.calculateFeedingData(
+        feedingActivities,
+        startDate,
+        endDate,
+      );
+      const age = differenceInMonths(new Date(), new Date(child.birthDate));
+
+      childrenData.push({
+        childId: child.id,
+        childName: child.name,
+        age,
+        data,
+        summary: {
+          totalFeedings: data.totalFeedings,
+          averagePerDay: data.averageFeedingsPerDay,
+        },
+      });
+    }
+
+    const overallSummary = {
+      averageFeedingsAcrossChildren:
+        childrenData.reduce((sum, c) => sum + c.data.averageFeedingsPerDay, 0) /
+        childrenData.length,
+      childWithMostFeedings: childrenData.reduce((prev, current) =>
+        prev.data.totalFeedings > current.data.totalFeedings ? prev : current,
+      ).childName,
+    };
+
+    return {
+      metric: ComparisonMetric.FEEDING_FREQUENCY,
+      dateRange: { start: startDate, end: endDate },
+      children: childrenData,
+      overallSummary,
+    };
+  }
+
+  private calculateFeedingData(
+    activities: Activity[],
+    startDate: Date,
+    endDate: Date,
+  ): FeedingComparisonData {
+    const days = eachDayOfInterval({ start: startDate, end: endDate });
+    const totalDays = days.length;
+
+    const feedingMethods: Record<string, number> = {};
+    let totalAmount = 0;
+    let amountCount = 0;
+
+    const dailyBreakdown = days.map((day) => {
+      const dayActivities = activities.filter((a) =>
+        isWithinInterval(new Date(a.startedAt), {
+          start: startOfDay(day),
+          end: endOfDay(day),
+        }),
+      );
+
+      let dayTotalAmount = 0;
+      dayActivities.forEach((activity) => {
+        const method = activity.metadata?.method || 'unknown';
+        feedingMethods[method] = (feedingMethods[method] || 0) + 1;
+
+        if (activity.metadata?.amount) {
+          const amount = parseFloat(activity.metadata.amount);
+          totalAmount += amount;
+          dayTotalAmount += amount;
+          amountCount++;
+        }
+      });
+
+      return {
+        date: format(day, 'yyyy-MM-dd'),
+        count: dayActivities.length,
+        totalAmount: dayTotalAmount > 0 ? dayTotalAmount : undefined,
+      };
+    });
+
+    return {
+      totalFeedings: activities.length,
+      averageFeedingsPerDay: activities.length / totalDays,
+      feedingMethods,
+      averageAmountPerFeeding:
+        amountCount > 0 ? totalAmount / amountCount : undefined,
+      dailyBreakdown,
+    };
+  }
+
+  private async compareDiaperChanges(
+    children: Child[],
+    startDate: Date,
+    endDate: Date,
+  ): Promise<ComparisonResult> {
+    const childrenData: ComparisonChildData[] = [];
+
+    for (const child of children) {
+      const diaperActivities = await this.activityRepository.find({
+        where: {
+          childId: child.id,
+          type: ActivityType.DIAPER,
+          startedAt: Between(startOfDay(startDate), endOfDay(endDate)),
+        },
+        order: { startedAt: 'ASC' },
+      });
+
+      const data = this.calculateDiaperData(
+        diaperActivities,
+        startDate,
+        endDate,
+      );
+      const age = differenceInMonths(new Date(), new Date(child.birthDate));
+
+      childrenData.push({
+        childId: child.id,
+        childName: child.name,
+        age,
+        data,
+        summary: {
+          totalChanges: data.totalChanges,
+          averagePerDay: data.averageChangesPerDay,
+        },
+      });
+    }
+
+    return {
+      metric: ComparisonMetric.DIAPER_CHANGES,
+      dateRange: { start: startDate, end: endDate },
+      children: childrenData,
+    };
+  }
+
+  private calculateDiaperData(
+    activities: Activity[],
+    startDate: Date,
+    endDate: Date,
+  ): DiapeChangesComparisonData {
+    const days = eachDayOfInterval({ start: startDate, end: endDate });
+    const totalDays = days.length;
+
+    let wetDiapers = 0;
+    let dirtyDiapers = 0;
+    let bothDiapers = 0;
+
+    const dailyBreakdown = days.map((day) => {
+      const dayActivities = activities.filter((a) =>
+        isWithinInterval(new Date(a.startedAt), {
+          start: startOfDay(day),
+          end: endOfDay(day),
+        }),
+      );
+
+      let dayWet = 0;
+      let dayDirty = 0;
+      let dayBoth = 0;
+
+      dayActivities.forEach((activity) => {
+        const type = activity.metadata?.type || 'wet';
+        if (type === 'wet') {
+          wetDiapers++;
+          dayWet++;
+        } else if (type === 'dirty') {
+          dirtyDiapers++;
+          dayDirty++;
+        } else if (type === 'both') {
+          bothDiapers++;
+          dayBoth++;
+        }
+      });
+
+      return {
+        date: format(day, 'yyyy-MM-dd'),
+        wet: dayWet,
+        dirty: dayDirty,
+        both: dayBoth,
+      };
+    });
+
+    return {
+      totalChanges: activities.length,
+      averageChangesPerDay: activities.length / totalDays,
+      wetDiapers,
+      dirtyDiapers,
+      bothDiapers,
+      dailyBreakdown,
+    };
+  }
+
+  private async compareActivities(
+    children: Child[],
+    startDate: Date,
+    endDate: Date,
+  ): Promise<ComparisonResult> {
+    const childrenData: ComparisonChildData[] = [];
+
+    for (const child of children) {
+      const activities = await this.activityRepository.find({
+        where: {
+          childId: child.id,
+          type: ActivityType.ACTIVITY,
+          startedAt: Between(startOfDay(startDate), endOfDay(endDate)),
+        },
+        order: { startedAt: 'ASC' },
+      });
+
+      const data = this.calculateActivitiesData(activities, startDate, endDate);
+      const age = differenceInMonths(new Date(), new Date(child.birthDate));
+
+      childrenData.push({
+        childId: child.id,
+        childName: child.name,
+        age,
+        data,
+        summary: {
+          totalActivities: data.totalActivities,
+          averagePerDay: data.averageActivitiesPerDay,
+          mostCommon: data.mostCommonActivity,
+        },
+      });
+    }
+
+    return {
+      metric: ComparisonMetric.ACTIVITIES,
+      dateRange: { start: startDate, end: endDate },
+      children: childrenData,
+    };
+  }
+
+  private calculateActivitiesData(
+    activities: Activity[],
+    startDate: Date,
+    endDate: Date,
+  ): ActivitiesComparisonData {
+    const days = eachDayOfInterval({ start: startDate, end: endDate });
+    const totalDays = days.length;
+
+    const activitiesByType: Record<string, number> = {};
+
+    const dailyBreakdown = days.map((day) => {
+      const dayActivities = activities.filter((a) =>
+        isWithinInterval(new Date(a.startedAt), {
+          start: startOfDay(day),
+          end: endOfDay(day),
+        }),
+      );
+
+      const dayTypes: Record<string, number> = {};
+      dayActivities.forEach((activity) => {
+        const activityType =
+          activity.metadata?.activityType || 'unspecified';
+        activitiesByType[activityType] =
+          (activitiesByType[activityType] || 0) + 1;
+        dayTypes[activityType] = (dayTypes[activityType] || 0) + 1;
+      });
+
+      return {
+        date: format(day, 'yyyy-MM-dd'),
+        count: dayActivities.length,
+        types: dayTypes,
+      };
+    });
+
+    // Find most common activity
+    const mostCommonActivity =
+      Object.keys(activitiesByType).length > 0
+        ? Object.entries(activitiesByType).reduce((prev, current) =>
+            prev[1] > current[1] ? prev : current,
+          )[0]
+        : 'none';
+
+    return {
+      totalActivities: activities.length,
+      averageActivitiesPerDay: activities.length / totalDays,
+      activitiesByType,
+      mostCommonActivity,
+      dailyBreakdown,
+    };
+  }
+}
diff --git a/maternal-app/maternal-app-backend/src/modules/analytics/dto/comparison.dto.ts b/maternal-app/maternal-app-backend/src/modules/analytics/dto/comparison.dto.ts
new file mode 100644
index 0000000..e6d0581
--- /dev/null
+++ b/maternal-app/maternal-app-backend/src/modules/analytics/dto/comparison.dto.ts
@@ -0,0 +1,76 @@
+export enum ComparisonMetric {
+  SLEEP_PATTERNS = 'sleep-patterns',
+  FEEDING_FREQUENCY = 'feeding-frequency',
+  GROWTH_CURVES = 'growth-curves',
+  DIAPER_CHANGES = 'diaper-changes',
+  ACTIVITIES = 'activities',
+}
+
+export interface ComparisonChildData {
+  childId: string;
+  childName: string;
+  age: number; // in months
+  data: any;
+  summary: any;
+}
+
+export interface ComparisonResult {
+  metric: ComparisonMetric;
+  dateRange: {
+    start: Date;
+    end: Date;
+  };
+  children: ComparisonChildData[];
+  overallSummary?: any;
+}
+
+export interface SleepComparisonData {
+  averageHoursPerDay: number;
+  totalSleepSessions: number;
+  longestSleepDuration: number; // in minutes
+  averageNapsPerDay: number;
+  nightSleepPercentage: number; // percentage of sleep during night (8PM-6AM)
+  dailyBreakdown: Array<{
+    date: string;
+    totalMinutes: number;
+    sessionsCount: number;
+  }>;
+}
+
+export interface FeedingComparisonData {
+  totalFeedings: number;
+  averageFeedingsPerDay: number;
+  feedingMethods: Record<string, number>; // { bottle: 10, breast: 5 }
+  averageAmountPerFeeding?: number; // if tracked
+  dailyBreakdown: Array<{
+    date: string;
+    count: number;
+    totalAmount?: number;
+  }>;
+}
+
+export interface DiapeChangesComparisonData {
+  totalChanges: number;
+  averageChangesPerDay: number;
+  wetDiapers: number;
+  dirtyDiapers: number;
+  bothDiapers: number;
+  dailyBreakdown: Array<{
+    date: string;
+    wet: number;
+    dirty: number;
+    both: number;
+  }>;
+}
+
+export interface ActivitiesComparisonData {
+  totalActivities: number;
+  averageActivitiesPerDay: number;
+  activitiesByType: Record<string, number>;
+  mostCommonActivity: string;
+  dailyBreakdown: Array<{
+    date: string;
+    count: number;
+    types: Record<string, number>;
+  }>;
+}