My seven year old daughter is very thin and we have a lot of trouble finding shorts to fit. These in size I, are perfect. They work for both gymnastics and as "monkey shorts" for under skirts. We couldn't be happier.
My daughter loves these shorts. They fit nicely and are great quality for the price. She is a 10 slim and the size medium fits perfectly, not much room for growth. But with this type of short, they need to fit well. I'm sure I will be buying the next size up as she grows.