Best way to lock down Android phone

[itstheyearzero]

DS is 11 and has just got his first phone. The contract I got him enables me to block inappropriate content but this doesn't work if he's connected to the WiFi, only if he's using mobile data. I'd appreciate some advice re the best/easiest way to make the phone safe when on WiFi. Thanks!

There is a Google parent app. You can set shut off times, permission for apps, even to do things like turn location on.