Um... technically...
Parents can give their own children alcohol in their homes. Some cultures introduce drinking wine (sometimes watered down) as part of the family meal. Totally legal.
Can't serve children in your home that aren't yours, except many states allow that if their parent is there and consents.
Businesses can't server minors.. except in Texas, of course. (Parent must be there.)
Learn more about the history behind the National Minimum Drinking Age Act, exceptions to the law, and the risks of underage drinking.
alcohol.org