>It doesn’t take a lot of effort

Sorry, but that's where you're wrong (at least, if you mean enforcing effective limits). What you're asking is for parents to spend their scarce time and energy on fighting a technical battle, against a system that is designed to capture attention, and kids with nothing but energy and time.

>But it’s pretty well controlled and they adjust to it

Or they did 10 seconds of googling and have all the access they want.