Sizes are roughly equivalent to age. If between sizes, order the next size up.
Measurements are in inches.
Your little girl wants to run, play, hop and skip just like any boy, but she also wants to wear cute skirts and dresses. The solution is to add girls under dress modesty shorts to her wardrobe. These under shorts pull up easily and are comfortable while allowing every little girl to hang upside down on the monkey bars and turn cartwheels without worry.
Sparkle Farms under dress modesty shorts have an comfortable elastic waistband which allows for some room for growth. However, they are meant to be form-fitting so that they are discreet under clothes. If you are having trouble deciding between sizes, order the larger size. When the modesty shorts stop fitting comfortably, simply pass them down to a younger girl.