That's between parents and their local governments. Yes when I was a kid my mom let me watch whatever and go wherever. The parent in my example ultimately decides what a kid may or may not do which is in alignment with existing laws. If the parent is endangering their kid that is up to them and their government to sort out.

Point being, put the controls entirely into the hands of the device owner. Options can be to default to:

- Block everything by default unless header states otherwise.

- Block only sites that state they are adult.

- Do nothing. Obey the operator. (Controls disabled on child accounts or make them an adult or otherwise unrestricted account on the device).

I think the options are just limited to our imagination.