[imok20]

Make him a language: let me elaborate. Use Python or Ruby and write a library of functions that he can call in particular ways that will make a "game." Let him learn how they work, and let him dive into the source code and figure it out and eventually make his own functions and classes and ... etc.

Discovery is the most rewarding part of learning to program, and having fast payoffs is always nice to keep a kid interested. Worked for me (I started with Logo around his age, but Python/Ruby is way better.)