Kinect Disneyland Adventures

For this you need to buy a costume at one of the stores (it autoequips).
The cheapest for Female character are 10.000coins (Jasmine & Tinkerbell's friends costumes) i would think Male will be same but cant confirm.
You can see stores on the park map () then Park map and select the area you are currently in and go to nearest one to you.
Note: Didnt unlock for me till i returned to the park.

EDIT: KACG SoMM pointed out in commented cheapest Male costume is also 10k coins

All you have to do is go into a store and buy a costume. Peter Pan makes you buy a Lost Boys costume. That's where I got the achievement at. I got it after I exited the store.

You will get this normally by progressing through the story, but if you would like to get this sooner, go to the shop on the map, at the northwestern corner of the bottom half of Main Street U.S.A. (Also, if you forget how to get to your map, hold both hands above your head and select "Park Map")


Go to clothing, then costumes, and purchase one. The cheapest one is 10,000 coins. When you leave the shop the achievement will unlock.