I'd be OK with an "I am a child" header mandated by law to be respected by service providers (eg. "adult sites" must not permit a client setting the header to proceed). On the client side, mandate that consumer devices that might reasonably be expected to be used by children (every smartphone, tablet, smart TV, etc) have parental controls that set the header. Leave it to parents to set the controls. Perhaps even hold…
A server header exists to say something is adult and could be used for user-generated content as well. [1] It just needs legislation and an afternoon from interns at assorted companies. It's not perfect, nothing is but could easily trigger existing parental controls and parental controls that could be added back into user agents. No third parties required. I think I've beat this horse into dust [2] so I should just h…
This completely leaves it up to the families / parents to control and gives some level of compliance to make the effort worth while.
There may even be a way to generate enough noise with the request to prevent any forms of tracking. This sort of thing should really be isolated in that way to prevent potential abuses via data brokers by way of sale of the information