See, what I'm curious about it why the OP feels guilty or bad.
Personally, if I had made that type of mistake, and it was literally a mistake and never intended to actually be a drink for the minor.... I'd be angry at myself for being stupid and ruining my evening. I wouldn't feel guilty about it.
Course given as others have pointed out that he ordered two beers when his only companion was underage and that he's here looking for a way for them to be in trouble. Yeah..