Raskullz Child Unicorn 5+ Helmets Meets CPSC standards and ASTM standards Fits size 3+ (fits head 48 - 52 centimeters) to 5+ ( fits head 50-54 centimeters) Nylon adjustable chin strap is comfortable and insures a secure fit The vented, aerodynamic styling allows for great velocity and a comfortable level of airflow At Raskullz, we live by one simple belief: Protect the Head-- Inspire the Imagination