Excellent idea! Why not check around to some of your local martial arts places and talk to them? If they've already got classes for toddlers, go in and watch one of the classes. Young kids have the attention span of a gnat, so great patience and short classes would be required. If they're leaning on the little kids like drill sergeants, and treating them like high school kids, opt out. And if they don't have classes for young kids, it would probably be best that they don't make all their mistakes on yours.

Sue