What about the sponge bunnies? Just don't teach him that one joke...
Ask him what kind of stuff interest him. He might not know of course, so if there are any magic shops in your area take him there and the guy behind the counter could give a few demos of what there is. There has been many good suggestions. Librarys almost always have atleast 1 good book on magic. Then there are those kits that come with a DVD, cups and balls, sponges, TT, silk, ect all the stuff for a beginner. And I know I have seen them created for your sons age range. I saw a good one for 40-50 I think. I will search for that link if you want it, and if I find it I will post it.
But I agree that maybe you should do the library thing first, to see how much interest is there. We all knew that kid who wanted to be a rockstar so his parents went out and got him a Gibson Les Paul (Really nice EXPENSIVE guitars... I love mine

) and he strummed it once and put it down.
Anyway, hope I have given some help.