On my recent trip to Cuba there were 10 high school students in the group, mostly girls. About 4 or 5 of them had trouble adjusting...to the food, to the "poverty" (which ain't nothin' compared to Mexico! So I thought it was just great in Cuba), to the lack of modern sanitation in some places, to homesickness. By the 3rd or 4rth day it just clicked for them, and they started to really like the place and to make good friends among the young Cubans. It was a real turnaround, if ever I've seen one.I sincerely hope that it works out the same for your visitors.
I can understand the boy being upset about the alcohol thing. There are no liquor laws in Cuba either, and I noticed that the young people there have a good deal less trouble with it than teenagers in Canada and the USA...which tells you something. Oppress people and treat them like babies, and they will act out against that oppression...often to their own peril.
However, there's nothing you can do about our liquor laws. Good luck.