Mark,
I would not say that there is one specific restaurant that is designated as the vegan restaurant. The bigger challenge is to find what restaurants are best suited to cater to his diet without him having to miss out on the flavors, cuisine, and fun of the experience.
I am not a vegetarian, but I have helped a number of friends who are. The first thing I recommend to them (and therefore to you!) is that you check the articles at
www.allears.net on the subject.
After that, I think that there are a few choices that lend themselves to your needs. Here is one for each park;
- Crystal Palace (Magic Kingdom)
- Tusker House (Animal Kingdom)
- Tangierine Cafe (Epcot)
- 50s Prime Time (Hollywood Studios)
But the most important thing is: call ahead.
For any table service restaurant wher you have reservations, you should not be shy to call ahead, ask for the chef, and tell them your dietary needs. They will guide you to what you want, and often will make special arrangements.
Go on. You deserve it. And so does your son.
Have a magical (and delicious) vacation!