There is a far simpler solution get him a camera with bellows, and let him shoot some images - he'll have far more fun, I did at that age, and my dad took his pictures to prove it. You'd be able to do the same and he'd love emulating you.
Originally Posted by mark
In those days my photography was cheap as I only needing imagination not film or processing, I usually took pictures of my new younger sister. This is actuallly a slightly serious post :-) I did have great fun and it was not many years later I learnt to process my first films, aged about 8 or 9.
So get him a camera, anything that looks fun, and he can see through, tell him to be patient and you'll get great images for his grand-parents.