Answer: I would talk with them and tell them that alcohol in moderation is completely fine. So long as they are the legal drinking age. And that their first time to drink it I'd like for them to do it with me so we can tell what negative effects it will have on them. That and we'd know their tolerance for it.
I would explain to them the negative effects of alcohol and encourage them to make the right decisions. I would also tell them that although they might get peer pressured into trying alcohol now, it may lead to an addiction in the future and cause them to have many problems.