Congrats....absolutely awesome. My 3 year old daughter loves kitesurfing. Used the B-2 trainer with a shortened bar and 11m lines with 3-4m extensions. I live in perth so its a bit strong for a 3 year old with full line length (20m).
Kids love flying kites (as well as big kids). Just get the right size/power for their tiny weight and the little buggers learn so quickly....
Riding unstrapped and unhooked, your son is way cooler than Sir Rowdy....