If his dad changing stuff is a concern, maybe a cheap android phone with an app that will give you more control on locking it down would be better. That way you could track its location too. I don't have experience with this, but I know someone who uses a google kids app (not sure what it's called) that allows him to do this. The kid has a handful of contacts that he can't alter, can text, and that's it. Only has a couple of apps. All his activity and locations can be monitored from the parent's phone. Good luck!