How to look like you're 10 when you're 13?

Hii, I'm a 13 year old girl, and for something for school I need to look like a 10 year old. I already figured put my hair in pigtails, and wear a big shirt to cover my chest, but what else? What kind of shorts and shoes, and are there any color or pattern that makes you look shorter? Any makeup techniques that make you look younger? Thanks a ton!