If the kids are not allowed into the place where alcohol is being served they are allowed to be there. The building does have to meet code, and have several means of escape, as well as a plan for security that will ensure that the kids are not allowed access to alcohol. We have done these. I don't give booze to kids.
Now there are places that allow 18 and over with armbands to indicate age. This doesn't really work, and we aren't doing that.