Hi there, Christiana!
I think you're going to be real happy with your decision to buy the Dining Plan with your vacation even though I can't think of a location that sells fries as a snack item any longer. I'm not sure if you've purchased the regular
Dining Plan or the
Quick Service Dining Plan, so I'm going to give you an idea on either one.
A majority of the the Quick Service locations at Walt Disney World have fries and cheese pizza on their kids' menus. You'll be able to use your son's Quick Service credits for those meals which normally come with sides like a small package of grapes, and a dessert. One of the other people in your party can eat your son's sides instead of [for example] the fries that came with their hamburger and your son could eat their fries. Once you run out of his child's Quick Service credits, you may just have to pay out-of-pocket if you decide to purchase fries as snacks. Most of the Table Service restaurants have fries on their menus as well. Check out AllEars.net for the menus on almost every eating establishment at Walt Disney World.
The snack options at Walt Disney World are endless...just look for the purple and white snack logo on the menu boards and in all the shops around the Parks and Resorts! Your son may just surprise you and decide that the little Mickey Mouse shaped pretzels taste so much better than the regular shaped ones!
I hope I've given you some good information to start out with. Please come back and see us if we can help answer any other questions!
Have a Pixie Dusted vacation!
~Jackie