Welcome to disABILITIES.
Michigan gave you some very good info. It would be helpful to know a little more about the child, since the advice we would give for a chld who uses a wheelchair and has only mobility needs would be a lot different than the advice you would get if he also has other needs in addition.
Things like:
Does he use a manual wheelchair or a power one? Is he able to walk at all? Is he able to sit without support, or does he need a special seat to sit? How does he communicate? What sorts of things does he like? Do loud sounds or dark places bother him? Does he have any back, neck or other health problems that would prevent him form riding the "wild" rides like Star Tours, etc.?