Take an earnest interest in your child's activities, both online and offline. Guide them how to behave in strange, even weird and scary situations with strangers. Be the reliable adult in their life to whom they can tell when they encounter something unpleasant, online or offline. Under the guidance of a parent your children will be safer than behind any amount of protective layers that these so called child-safety apps provide, and they will also know how to help their friends to navigate risk and avoid danger.
Or put another way, if your child must eventually swim in the sea, would rather that they know how to swim, or strap a fifth flotation device onto their back?