For iOS, start with Apple Screen Time/Family Sharing and consider Bark for alerting on risky texts/social activity; for Android, use Google Family Link plus a reputable suite like Qustodio, Net Nanny, Bark, or Norton Family for deeper app/web controls and location. Key features to compare: real-time location with geofencing alerts, app/website blocking, screen‑time schedules, activity reports, social media monitoring (note: iOS limits this to notification-level data while Android allows more with proper permissions), suspicious keyword alerts, tamper alerts, and responsive support. Use these only on devices you own with the child’s knowledge and in line with local laws and store policies. To tailor a recommendation, what device models and OS versions are your child using, and do you need actual message content monitoring or just usage summaries and alerts?