Personally I do not believe this is a solved problem. Technically maybe, in practice not at all.

It is quite a job juggling the controls of the different companies. Microsoft even has two, one for Xbox one for windows.

And then your child turns 13 and your only option is to take away the devices entirely.

Another thing already discussed is school provided hardware. I know the schools try, but it is usually one person against 300+ students trying to figure out how to game/hack the system. Eg there's no reasonable way where you can expect one person to maintain a YouTube channel whitelist.

I do agree that we might be solving this issue the wrong way, but there is a definitely a problem here.