Instructables member Shawn Melito designed and built a special "water scooter" for his then-5-year-old daughter, who has Cerebral Palsy. This gave her buoyancy, mobility, and independence on the water -under supervision, of course. He explains how he he built at at the link. Then comes the kicker:
BTW - After two seasons of use my daughter has grown out of this, but it still works great. It is free to the first person who has a disabled child the right size that can use it safely. We live near Toronto, Ontario.
Link -via NeatoBambino