Rehd
I started paddling with my 6 year-old daughter this year by sticking her in the front of my Prijon double (plastic). I had to have her sit on a "cushion" throwable PFD so that the cockpit was lower than armpit level on her. I also got her a cheap screw-together kayak paddle that was her size. The size of things was the biggest issue.

One thing I have seen for teaching beginners how to roll was a length of PVC pipe filled with material to make it weighty (sand, etc.). The tube is capped on both ends and is hooked with straps around the deck so that it sits lengthwise along the keel. It serves as a "weighted keel" so that people learning to roll have a little extra help. With kids, it could make the yak nearly rollproof while they are getting used to things.

Just a thought.

Marcehl