I had oral surgery when I was about 13 to remove an permanent tooth that never developed... I remember it only taking about 2 or 3 days to recover.... The only thing I would be concerned over is if the tooth will be pushing his other teeth forward. Emotionally this will be very difficult on him. (Just remember how mean kids can be) Find yourself a great pediatric oral surgery dentist and get them removed. I found this for you:
Complications of supernumerary teeth can include delayed and/or lack of eruption of the permanent tooth, crowding, resorption of adjacent teeth, dentigerous cyst formation, pericoronal space ossification, and crown resorption. Early diagnosis and appropriately timed treatment are important in the prevention and avoidance of these complications.
Good Luck, but do it sooner than later!
B. : )