I have 3 daughters and they are too old now for the costumes but in years past all 3 have dressed up together. We have Belle, Ariel, Jasmine, Megara, Cinderella, Aurora, Snow White and Minnie costumes. Some were passed down to one another. The costumes were their one major purchase I gave to them whenever we vacationed there. I thought it saved me a lot of money considering how much merchandise there is for kids to want!
Just speaking from a mom's point of view, the fondest memories I have are when my girls dressed up together and all the fun they had. I have some of the cutest pics, one of my youngest dressed up as Snow White when she was 3, in the Liberty area in the Magic Kingdom, where they do the sketch portraits. There was a cart of fruit for sale nearby, and she quickly eyed the apple and begged to have it. A visitor thought it was so cute that they asked if they could buy her the apple.I have a few pics of my little Snow White eating her apple and the cute comments the nearby CM's and visitors had for her.(okay some of you are rolling your eyes but I thought it was adorable).
Anyway, kids are only kids once, let them enjoy the fantasy and the dressing up if they choose. WDW is the one place we can forget about the real world and lose ourselves in the magic.