Of course he fractured his foot and has a walking cast and we leave in 6 days for our next trip

We are going to see if he can handle walking and if not we're renting the poor kid a wheelchair.
Just so you are aware, the WDW wheelchairs are adult size and may not be very comfortable for a child.
They are quite wide, with sling seats. If you put 2 kids in one wheelchair, their weight tends to slide both down to the middle of the seat together.
Also, the footrests would be way too low for your son to rest his foot on unless he's a really big 8 yr old, so the foot would be hanging there unsupported.
If you think he'll need a wheelchair, there are some places listed on the disABILITIES FAQs thread that rent child wheelchairs or special needs strollers (kind of like giant umbrella strollers).
He might also do well in a WDW stroller - the double would give him more room.
Thank you all so much! I was thinking about the stroller thing too but assumed they would be to small. .........................................LOL I wish they made something that does not look like a stroller for the older kids.
Thanks again, Lisa
The WDW strollers are large and don't look like regular strollers. If he's too big for a single WDW stroller, you can always rent a double. Here's what the WDW strollers look like, single and double (picture from allearsnet.com)
Also, keep in mind that "I'm tired" in kid language often really means "I'm bored", so he may do much better than you expect.
We took my niece and her not quite 4 yr old DD with us one year. She didn't have a stroller with and we didn't mention the possibility of a stroller. On the 4th day of touring, she said "My legs are all out of walk." That was the first time she had complained and we did get a stroller after that. I think if we had not done 4 days in a row, she may have been able to do the trip without a stroller at all.