I think it's a great proposal if we add a slight alteration. Rather than requiring parents to maintain block/allow lists, the OS should allow the parent to lock in a birth-date, and that birth-date is used by the system to generate a user-age header, from there, websites can be legally required to respect the header and maintain whatever restrictions correspond to the applicable laws. This gives sites the ability to dynamically adapt to users, changing features and laws, as well as remove the burden from the parents of having to determine which sites are safe and not.