I think its preposterous not to allow minors to drink if their parent is there.
alcohol has such a taboo in the US, and that is why binge drinking happens. i can drink legally and even then my parents don't like me to have a beer. if i have a .22 when I get off work, my dad accuses me of being an alcoholic. when i pound a few jaegerbombs with breakfast I get these funny looks. just kidding about that last one, but its lame.
the only way to break the taboo is to eliminate the stigma associated with alcohol and young people. I curse around my parents, talk about sex, and am pretty comfortable with them, but they do not approve of me drinking just cause I had one alcoholic grandma.