Disney dosn't have fries listed as a side anymore for the kids meals. Most people, when ordering anything, will just take what is on the menu listed. So it's an effort to get kids to eat healthier. However, there are kids out there who aren't not particularly fond of eating healthy so fries are available. Fore example, "I'd like the kid's cheeseburger meal with fries" is one meal since they will leave off the fruit or whatever else is listed as a side.
However, if fries are served at any place, you can order them separately and pay for them separately.