Well, communication is the primary feature I would allow.

Back in my days it was typical for us to run to the phone booth "mom, I'm still out playing, will be late for dinner" Now there aren't phone booths anymore.

The concept of the kids messenger by Facebook sounds right. Quite risk free communication, which allows giving the kid freedom without having to always look over their shoulder what they are doing.

As said: that being not from Facebook would be great!