This patient support community is for discussions relating to allergies, behavior, developmental disorders, immunizations and vaccines, puberty, and any other pediatric health issues including brain, bone, heart, lungs, gastrointestinal and urological in adolescents, infants, newborns, and toddlers.
I remember in school when I would get uncontrollable erections like most boys I guess, I would put my belt over it and pull my shirt out to hide it.
You can do the same by belting it close "not tight" to his body and buying him some extra large T-Shirts, that should solve the problem for the him and you.
Be fore-warned though that he may ejaculate at any time due to the fact that it has to come out. Thats what we boys called "Wet Dreams" before learning to masterbate to relieve that problem. If that becomes a problem you may want to try a Condom.
Hope this helps, sounds like you have your hands full, but again I say no to drugs. :)