I agree with the Power chair.
My daughter was 2 yrs old when she got her power wheelchair. She has a very rare genetic disorder and has contractures of her wrists, hands, elbows, etc. She didn't have much strength or stamina. That said she could drive that chair like a pro. They got a mini joystick for her. The entire chair could be controled with one finger. Hydrolics and all. She had total control.
Now that she is older she has a regular joystick. Power chair options are amazing... from head controls to touch screens, regular joysticks to mini joysticks that can be controled with a finger. Make sure he goes to a good clinic that talks about options and not just orders something generic out of a book, get a demo. EVCs, not to much. Power Chairs are also much easier to transfer in and out of without worrying about getting that one leg around the controls, etc. Its just a better option for people with health that will continue to get worse.
Good luck to you and your family!