Phone Safety App for Littles

Recently, one of the littles in my partner's systems downloaded a streaming app and signed up for it using his credit card. He is now 60 dollars overdrawn. What apps can you guys recommend to protect his money and to censor what the littles can do or see? His phone is a Motorola (Android). This app would have to be free or cheap. Thank you!

What is he trying to stream?.

Have you tried parental control on the phone so that it limits the apps in play store to appropriate age groups?