> These devices could send headers to websites saying "I'm a kid" -- but this system doesn't exist

And there would be ways to work around it. If people find that privacy-preserving age verification is not good enough because "some kids will work around it", then nothing is good enough, period. Some will always work around anything.

if a parent gives a kid a full on smartphone, charge the parent with child abuse just like feeding the kid alcohol, cigarettes or having sex with them. people will catch on.