Let me also send a big
and second RustyScupper's thoughts on the possibilities within give Kids the World Village. I suspect by now you have read the GKTW materials. It is truly a wonderful place. My wife and I are also volunteers there and can attest to the dedication of everyone we have met.
As far as the parks, while I can't give you specific "special" thoughts I can offer a couple of suggestions. If your son is into animals then Disney's Animal Kingdom will provide opportunities for viewing and in some cases interacting with animals. The Safari ride is fun and there are two major walking trails that are typically not very busy and good opportunities to see animals. There is the Affection Station over in Rafiki's Planet Watch which you get to by riding a train. It is usually not very busy and gives the opportunity to interact with some animals. One warning, stay away from It's Tough to be a Bug. Loud and scary. Same for Dinosaur. The Dinoland area might be interesting to walk around but stay away from the Dinosaur ride. Very loud and very scary.
SeaWorld is worth considering if your son finds sea life interesting. SeaWorld is a less intense (except for the roller coasters) and typically less crowded park. There are a places where your son could touch sting rays and maybe a dolphin. Lots of places to view sea life.
As far as the other Disney parks, a visit to the Magic Kingdom is the typical focus of a Disney visit. It can be a bit busy though the days your are visiting typically see lower crowds. A walk down Main Street, seeing the Castle, meeting Mickey Mouse and the other characters are all special. Note that Mickey and a few of the other Disney characters come to GKTW on Monday and Thursday mornings. If your son has a special Disney character mention it to GKTW and they will do their best to make it happen. If you decide to visit the Magic Kingdom there are a few attractions that are lower key, quieter, that your son might enjoy. I find the attraction descriptions at Allears.net to be very helpful:
http://allears.net/tp/mk/mk_attr.htm
I imagine that you have a lot to do in the next few days to prepare for your visit. I will second RustyScupper's thought that GKTW does everything it can to make your time there fun for you son and as relaxing for you as possible.
Wishing you a smooth and happy trip!