It should not be too difficult to match respective adult/maturity laws in any given jurisdiction via IP access - as there are different laws as far as what constitutes "adulthood" in relation to sexual engagement. Via VPN these could be circumvented - but that is an intrinsic problem that the internet structure has as a whole and it is not really easily solvable.
I guess parents and concerned adults are somewhat victims of technology that is not easily containable anymore. A very deep philosophical issue that any community can probably only solve "locally" through whatever consensus mechanism...