I went to a circus once and they had a girl do this. At the end of the show I told her I would cry if she didn't tell me how they did it (I was young btw) and she told me she liked it when kids cried...Lol weird memory
But this one was pretty obvious, her dresses kept getting smaller so there's probably a clip on the back for it to just slide off, the girl I saw was wearing a skirt and would change into pants and stuff I was like