P.G.
I don't think you're being silly, but I wouldn't assume either. I would find out if other young adults have been invited and if they THOUGHT about the alcohol issue where the kids were concerned. Have the conversation, and then make the decision from there.
Edit-not all bachelor parties are "Bachelor parties" - my hubby and his friends all played multiplayer video games for his bachelor party; another of his friends was taken to Dave and Busters, so it's possible this is more a "guys bonding" than the traditional "skanky" bachelor party.