We just did this today and it was so much fun!
We thought we had a great plac to view the parade from. It was a nice bench AND in the shade on a hot day. Well I saw a castmember in a pair of blue overalls and knew he was from the parade staff. I told my son about people being in the parade and asked him if he wanted to try it. So he runs over and asks if we can be in it. We all did it (DD 6, DS 8, DH and me.) They do have a minimum height requirement of 46" and you have to sign a liability release but we did it and wore tutu's and marched with the hippo and the elephants. Got the pins too which was a nice surprise. I tried to take photos during the parade and got the backs of the kids but at least I have something to prove we did it. I have a great photo of my DH in his tutu for future blackmail.