I have to say, I think it's a great idea. I might be more inclined to be more patient with someone I know is a minor. And that aside, they really DO need different advice and a different spin on things.
It does make me uneasy, as others have said, that people as young as 12 and 13 are talking with a lot of adults over the internet, but short of policing the parents, I think giving them a special title as a "heads up" would be a good thing. Let's be honest- there are people who act like they're 13, but are not-- these people need a different sort of advice than the people who act like they're 13 because...they're 13.