"Jumping" anyone is a fucking asshole thing to do... It wasn't the right thing to do. You should have told your friend that IF he tried anything again, that HE should do something about it, insted of rounding up a gang of naive teens to nearly (and possibly) kill the guy. Especially when it couldn't have even been proven that he was trying to "pick up" a 7 year old... How could you know... what was he saying exactly?

You don't know, do you?