The younger kid's chat is disabled. not allowed to friend anyone.
The older kid has chat enabled, but is only allowed to friend people we vet.
Computers are in an open area, chats have been keylogged, we check occasionally.
If friends show up unanounced, or they chat where they're not supposed to, they lose internet access long enough to regret it
When they get old enough to have friends online, we contact the parents, make sure they're compatible politically, theologogically, just generally not extremists and their kids have some base level of dicipline and are safety minded.
We also semi-regularly play with them and set rules about the appropriateness of the games in relation to the kids ages. The younger one's don't get to play the violent ones.