Bell Alibi Youth Bike Helmet Size-adjustable child's bicycle helmet perfect for cruising, recreational touring, and recreational MTB Universal size fits head circumferences of 50 to 57 centimeters / 19.75 to 22.5 inches Durable and protective Fusion In-Mold construction with 23 cooling air vents ErgoDial fit system and Cam-lock levers for simple size adjustments; PinchGuard buckle CE EN1078, CPSC bicycle certified; one year warranty