What about just outright banning them from online chat rooms/sites? If they are proving that they are unable to follow the ground rules you've established, then they are not yet mature enough to be given this much freedom/responsibility. That's kind of where I've arrived with difficult child 1 because of his penchant for porn (even on my iPhone I've caught him looking at stuff on YouTube). He only gets on the computer when I allow him access through HIS account, and that account has severely restricted internet access (his school website, his grade website, and I think one other kid's website). Everything else is blocked. When he earns back my trust, he gets the privileges back.
