Congratulations to your nephew. What a good reward!
He definately won't have the stamina to walk a whole day at MK, so he will need something to help him.
If he just learned to walk at 8 years, he probably already has some type of mobility device (either a special needs, large size stroller or a wheelchair). You just may not be aware of it since they may not bring it along to family gatherings.Anyway, that's the first thing I would check into. The next would be to see if he could borrow one from the day from the school district, an equipment lending library (United Cerebral Palsy often has these). I assume he's been working with a Physical Therapist; he/she could help out with arranging this.
If nothing else, you could
rent a stroller for him at the park; Safari Steve (a MK CM) has posted that they have different sizes of strollers and the largest will fir up to a small 12 year old. If he uses a stroller or a special needs stroller, make a stop at Guest Services to get a Guest Assistance Card that will allow him to take the stroller into lines. You would have the option of him walking in line, but if the wait is too long for him to walk or the line has stairs or other things that he will have trouble with, you can bring the stroller in. Depending on his other positioning needs, a regular stroller may not be comfortable for him. You could also rent a wheelchair at MK, but they are adult wheelchairs and would not be that comfy for a small 8 year old.
Just in case you wonder, you can't rent an
ecv (motorized
scooter) for an 8 year old. You have to be at least 18.
Good luck and here's some Getting Everything Organized Pixie Dust to help you.