The Judges Tent in Mickey's ToonTown Fair always has Princesses there. I think Cinderella is always there, and then the other two rotate, and one may or may not be a Princess. The pic in my sig is from the Judges Tent. Belle was the mystery guest when my brother and I stood in line. The mystery guest changes. I've heard of people seeing Mary Poppins, Prince Philip and other non-Princess face characters there. If they're going before Cinderellabration ends, they could watch that, although there are not meet and greets. Storytime with Belle in the courtyard of the castle also has a meet and greet.
If they really want to dine with a Princess, 1900 Park Fare dinner is a monorail ride away at the Grand Floridian and Cinderella is there with the mice and Prince Charming for dinner.