TMB – I still don’t see what non-Jewish marriage practices (and for the US pretty weird ones at that) have to do with Yidden giving or not giving alcohol to underage children. As far as I can see, there are two separate issues:
1) Is it legal? In most states giving alcohol to someone underage who is not your child is illegal. Since dina d’malchusa dina, we therefore can’t do it.
2) Is it advisable? As many posters have pointed out, alcohol is a potential hand grenade for a teenager. Some people may know their own children well and feel that a small amount won’t hurt. Certainly a non-parent like a Rebbe shouldn’t have that choice. One factor that has only recently been shown by research – the parts of the human brain that deal with judgment and impulse control don’t mature until the person is in their late teens, even early twenties. So not only may a teenager not be able to judge whether/how to drink, it could also in excess interfere with the brain’s functional development.
And, of course, a teen who drinks alcohol is much more likely to try other “good stuff” like marijuana and cocaine.
So what do we need it for? When I was a kid grape juice and soda pop were fine. What’s changed?