The Candy from last year was a variety of different things, Mostly things like lollipop, sweettarts, and Nestle candies, Don't forget, you can go to the stands pretty much as many times as you want as long as you get in line, So if you find a lot of nut candies, go back to the ones that were not.
As far as dining, most of the buffets have things like chicken nuggets, Mac n' cheese, hot dogs, some have pizza. These all should be safe for your son, but when in doubt, ask a server, they will be more than happy to assist you. Calling ahead for sitdown meals is also a good idea.
I hope that your sons and your visit is everything and more than he is hoping for.
Diane