Don't isolate them. Kids kept in a cocoon of safety may not connect with a group. Kids need a group. Don't trust them unconditionally. Operate on the assumption that any kid, regardless of history, is capable of a lie.
Peer groups are powerful things and can challenge values and behaviors.
Don't use them as go-betweens. Do your own communicating with teachers, secretaries and others. Don't take much at face value. Schools are rampant rumor mills. Kids love to gossip and embellish.