-- Last Updated: Feb-04-13 4:46 PM EST --
What sort of kayak do YOU paddle (tour sit inside, SOT, etc.)? Does your son want to "get into" kayaking meaning is he excited, willing to get wet and have fun learning or just go out now and then?
A SOT is definitely easier if he just gets out now and then but there are some nicely scaled down models (not just shorter) that give kids a "real" kayak experience.
I've heard folks speak well of the Wilderness Systems Piccolo which seems to be no longer made but may be found used. Currently they offer the Tsunami SP which may be a good fit.
I think ideally for any boat you want to avoid one that is too wide making it hard for short arms to reach far enough for good strokes. 22" or narrower isn't a bad choice for a kid -- would be like 26" or more for adult. Narrow also makes it easier for them to play around with edging.