A husband and wife recently threw a birthday party for their son at their house and unwisely served some alcohol to the teens in attendance. The young people had a good time and fortunately no one was injured, got into an auto accident, or suffered any ill-effects. But the large party got loud enough for some neighbors to call the police.
The parents were arrested and each was sentenced to eight years in prison.... a total of 16 years in prison for the couple.
It is clearly both illegal and unwise to serve alcohol to anyone else's child, even with parental permission, snd even if the "child" is an adult under the age of 21.