For example, all devices could require your ZKP ID attestation to be usable unfiltered. Then the relevant apps/sites would be equally inaccessible to children. And then you remove the ZKP ID attestation because the device owner (parent, school, etc) already knows when the user is a child.
ZKP ID would work but that’s essentially deanonymization because you have to provide your ID to someone though no one has total information. Also just checking for its absence doesn’t work because that’s opt in and less than 5% of parents would do it. Every individual, irrespective of age would have to have a valid one.
That said it was funny, yesterday Microsoft said I had to age verify my account. I went in basically with the intention of backing out of it at the first sign of over reach.
First step was, 'provide you email for this account'. So I did that and then... approved! You are certified over 18+. That is the flip side of this, some of these companies will put up some of the weakest barriers on this stuff.