13 year old stepson's iPod didn't get any internet access for a month after last battle.
Technical solution for filtering is a joke - if you can take the devices OUT of their rooms and make them use them in the lounge/shared area.
Any rubbish with them not following the rules change the wifi key - no access at all for a week.
Internet access is a privilege, not a right. If they can't follow the rules they lose it. tough biccies.