> once you give a teen a smartphone your control over what websites they visit ends.

Isn't it pretty easy to set up a whitelist of apps/websites kids are allowed to use?

Whether or not that's a healthy thing for your parent/child relationship is a different question.

> But also: cutting one kid off from social networks ostracises them. The parents recognize it's a collective action problem.

OP already gave you your answer, you just chose to ignore it

Not easy. Kids can bypass very easy. Like those security-theatre apps companies use - but crappier. Then, once on a site/app like Instagram or Roblox it's a whole other layer of whitelist to manage (if possible).

It's simpler to take the phone away. And iPad. And stop hanging out with your friends that have it.

Phone management is hard to solve for pre-teen and teens.

It's like taking heroin away from an addict. They hate you for helping.

on iOS this is basically impossible