>but some times their children is in care of a school?

And not only that but some of those times are dinner break, on a school campus with a thousand other kids and barely any supervision. Even if phones are banned, it's easy to hide one and for a child to be showing their friends unhinged stuff they found on 4chan.

And some of those times are on a bus carrying at least 50 kids when they're 'supervised' only by a driver ... and so on.

>Even if phones are banned, it's easy to hide one and for a child to be showing their friends unhinged stuff they found on 4chan.

That would still reduce ther exposure by 1-2 orders of magnitude, which is perfectly acceptable.

I mean, we all saw the occasional heinous stuff, goatse, lemon party, etc, that doesn't ruin you. I don't think preventing them from ever seeing anything disturbing is a realistic goal. It's more an issue when kids are allowed to be fully addicted on an ongoing basis instead of spending their time doing things that help them grow. I think keeping them from spending all their free time on youtube or in Roblox is more the goal.