My son uses a potty seat at home that folds but its still pretty big. Does disney have smaller toilet seats for little ones? I'm hoping to not bring it.
My guess is if they do have that it would likely be in the women's bathroom. (not being sexist, just realistic) I know I have never seen anything like that in the men's room except for significantly lower urinals. My local library has a toddler size one in the men's room though and that's the only place I have ever seen one in my life. It's the cutest little toilet I have ever seen. About half the size of a regular one. Just damn cute. It's like something from a doll house.
EDIT: Come to think of it though, since I'm not in the habit of looking into random toilet stalls, there might be something that I just never noticed before. Guess, I didn't help much with my answer did I?