[stomachmonkey]

Had plenty of these as a youth.

Sometimes "word" gets out and the party grows on its own.

Would have gone over to "check in". Everything cool, kids under control then tell the neighbors son to call you or come get you if things get beyond his ability to handle. You'll simply show up "unannounced" so he does not lose face.

If you went over and it was already getting out of control then you shut it down. More than likely if the kid is as you say a good kid he'd appreciate it.

Regardless, showing your face sends the message that the event will be brought to parents attention which should help keep things under control.