Glad you like the idea Joe. It occurred to me as I was writing the reply so give credit to Bill for asking!
Good points about strapping someone to an airboat. Just don't do it.
Bill & Carol - Please make sure you have some eye protection for the kid. I'd strap on a bunch of flotation (acts as body armor too in case of collision with debris or the ground) and hang on to the kid. Taking another idea from the animal world... I've got a PFD for my dog - that has a large handle on the back of it. I can (well COULD before the dog grew to be over 120 pounds) pick up the dog using the handle. I'd take a child's PFD and sew on some extra webbing so it has a handle or two on every side for gripping from every angle. Just don't tie them down!!!
one other thing to consider in the child seat on the footstand - the bugs, spiderwebs, seeds, debris, etc. You don't want to put the kid right in the blast zone!!!
We know you are an extra safe driver - But like Randy says - they don't call them "accidents" because they are planned in advance!!!
Way to go!! ::hi-5:: for introducing them to the outdoor world from an early age. They'll be well adjusted when they grow up for sure!