Obviously I shouldn't post in the wee hours of the morning, because in reviewing the thread and my response, I want to clarify:
1. In some states there is an underage drinking exception for religious ceremonies. However, since this case involves beer, I can't imagine what religious ceremony might be involved. (Octoberfest?)
2. In some states, parents can consent to an underage consumption and service of alcohol. Some states require that the consumption be in the presence of the parent, and since this involves some "partying", I would question whether the parents were actually witness to the consumption.
3. Really the legality doesn't matter in this case. The troop pledge signed by the scout and his parents is controlling. If you don't enforce the pledge, then don't expect the boys to listen or believe anything else you say to them on any topic. If you don't enforce your troop pledge now, equal application and consistency in enforcement will become impossible in the future. i.e, would maijuanna use block advancement, how about DUI, what if they just have a statutory rape problem? what if one is a misdemeanor and one a felony?
On a personal note, my husband and I once sat at a wedding where parents insisted that their 16 year old son be served champagne and wine. (With parental permission it was a legal request in the state.) It was surreal because the child had already been in residential treatment for drug abuse. When the waitress balked at serving a minor, my husband and I (both lawyers) were consulted about the legality of the underage drinking. We had to say it was legal, but we expressed strong opposition to the use of the alcohol by underage children, especially those with a dependency problem. We were nicely told to mind our own business, after all these were "nice parents from a good neighborhood, who otherwise had good parenting skills. The boy had just been experimenting with drugs and gotten into a little problem...After all, haven't we all done something stupid as kids?" It's now 5 years later and the boy has been dead for some time...alcohol and drug abuse.