My three daughters wore princess dresses to goofy's kitchen and then to ariels grotto. We didn't let them wear them in the park on rides because they are too uncomfortable and itchy. My daughters wore the red belle dress (age 7), ariels wedding dress (5), and tinkerbell (2). They have the WHOLE costumes including wigs, but we only allowed them to wear the dresses and shoes. It was a great experience for them and I wouldn't have wanted it any other way. While Belle was at our table, the Beauty and the Beast song started to play. She asked my three girls to come dance with her.
Here is the pic:
I agree with aggie though on letting them know that not all princesses will be there. We were waiting for cinderella and she wasn't there. All was good though. It was the best character dining experience we have had. Definitely worth the time and money.