Make android kinda dumb

I am thinking about getting a phone for my son.

There are some really cheap android phones around.

But I also want to restrict what he can do on it while he is still young.

I was thinking something like net guard but with a password, so the settings can't be easily changed.

I could just get a dumb phone, but I also have some old android phones hanging around.

What options are there for this kind of app/network control?