OMgosh... I just LOVE the peter pan idea!!! It would be simple and not too much fuss with the horse costume!!!
You could make the hat out of felt from Wal-Mart.. it' wouldn't cost but a couple bucks to make!!!
You could be one of the boys from the movie, Peter!!! Wear button down men's PJ's and some hairy potter glasses!!!! It would be a snap to put together!!!
Or you could find a union suit...and carry a teddy bear and be Michael!!!
I'm going to keep that idea should I ever need it!!!!