With added features to keep them safe and stylish Rear sizing dial with integrated light Fidlock clasp technology for pinch free opening and closing Adjustable side locking dividers Small helmets fit heads 48-54cm Medium helmets fit heads 54-58cm An essential for all scooter and bike riders Adjustable spin dial for the perfect fit Extra padding for comfort and safety Air vents to keep heads cool Conforms to EN1078 Safety Standard Please choose the size carefully - measure the full circumference of your child's head.