> Allowing parents to configure their children’s devices to block services that require users to be older than the specified age or that do not provide an age rating.

This could be done with setting the age too. Kids don't have their own money and can't sign their own cell contracts, their parents do, and during the phone setup process, the parent could set "the owner of this phone is a minor" checkmark, set the age of birth (so it auto "unlocks" at 18), add a parental password to manually unlock for whatever app needed (or reset or change the setting). Then the phone would just send "user_is_a_minor" flag to whatever and/or filter the 18+ stuff.