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…
Worse, it leads to situations where society seems to want to flat out be kid free in many ways. With families reportedly afraid to let their kids walk to and from school unsupervised.
I don't know an answer, mind. So this is where I have a gripe with no real answer. :(