Check out the Adjustable GelShell! Sizes range from Youth, to Adult Small, Medium, Large and X-Large.
The Adjustable is great for all ages, all sports as the adjustable band allows for multiple sizing options with one GelShell! Also, it's pretty cool as it allows room for a ponytail to exit the rear of the GelShell!
Youth size fits 14 1/2" - 17" Circumference, typical ages 4 - 7 years old for both boys and girls!