the opinions here have turned into orders of how individuals expect your son to go.
You will utimately make the correct choice. Everyone here has an opinion, some strong, some annoying, but overall there should be enough fuel for you to work something out.
Having said that heh, I agree with having something like java or java-script as a start, but java is close to C.
If he wants to see big explosions on the screen in 5 minutes, learn flash. If you know he has patience, learn some c/c++ with him, that way he and you could explain concepts to each other as you go along. 2 minds are better then one in some parts of the world
I agree with the guitar concept, as having spent some time with children in tutoring in sport before, thats exactly how children usually are. If they love something, they''ll jump on it, otherwise it can be boring in minutes.
My opinions
hope you and your son fair well in his future endeavours!!
HAILS
http://on.to/oni