You’d think that one could simply block sites that don’t have the age header set on child computers. This may block kids from hobbyist sites that don’t bother to set their headers as kid-friendly, but commercial sites would surely set their headers properly. Over time sending proper rating headers would become more normalized if they were in common use.

This still isn’t perfect, as it creates an incentive for legislators to criminalize improper age header settings and legislate what is considered kid-appropriate. But it’s still better than this age verification crap.

Yes, that's how parental filters already work. They use a combination of rta tags and external data to block pages. Even works with Google safe search, firewall devices, etc. The rta ecosystem is already built out and viable.