Shouldn't the verification be other way around? That is, you need to prove that you are a child. Then the site can present you more strictly filtered content. Parent can sign child's device on first boot, token stored in TPM so that it's hard to remove.
It's basically the same type of enforcement on sites, as they need to verify and filter content for children, or just block them. Most of the internet users are adults, why not make internet for adults by default.
So you want porn on every web site and have kids prove that they're kids by issuing their school card (because they won't have a real id yet) so the porn get hidden for them or so they get entirely banned from the system?
Nobody's ever gonna show an id to get banned from a website.
Do you see porn on every website right now, since we don't have widespread verification yet? The internet was designed for adults from the start, only in recent years we got a significant portion of kids on it.
The thing is that if you are a kid, your device would be bought and signed by your parent, you have no way of refusing to show ID cause device does it automatically. Of course there is a problem that children could use parent's phone but that's also a way to circumvent current age verification propositions.
The idea is just to sign device once for a kid and let them use it without constant worry.
It's basically the same type of enforcement on sites, as they need to verify and filter content for children, or just block them. Most of the internet users are adults, why not make internet for adults by default.