Don't worry, it will be fine! My DD has CP (mild) and must use a chair in the parks. When she gets to the end of the line she hops out and dashes (as fast as she can dash...) to get on the ride. We just get lots of grins and smiles. She couldn't enjoy the parks without the chair and neither could the rest of the family!
We were talking about it today and if we can, we are definitely going in August...he just has to stay healthy (where is that knocking on wood smilie when you need it?)