> Kids shouldn't have tablets or smartphones or personal laptops before age 16.

If you make such a restriction, they'll secretly buy some cheap "unrestricted" device like some Raspberry Pi (just like earlier generations bought their secret "boob magazines").

Parents should have an allowlist of devices to be able to join their network. And then they can require root certs or something for access outside of a narrow allow list. There's a host of ways to solve both problems. Just remember to check for hardware keyloggers on your (the parents') devices, as kids could use them or try evil maid attacks, etc. if they feel totally encaged.

I've said it before but prohibition works, if the goal is to reduce usage. I don't see this as a realistic problem.