I was surprised about the lack of kids dressed up in DL, frankly. In WDW the numbers are certainly greater.
When we went to Ariel's, DD was the only one there in a costume. And the room was full. She was wearing sleeping beauty. While I saw others in princess themed clothing, none had the costume on.
We talked at length about how/when she was going to wear the costume and decided to bring it with us and check it into a locker and then have her change right before the meal. She then wore it all night after that. She did get lots of attention! It was a bummer, because sleeping beauty wasn't one of the princesses that day, but she was fine with all of the attention. In fact, I think she got more because the other princesses knew sleeping beauty wouldn't be there.