●XS:46-50CM Recommended Age:Baby and Toddler 1-3 Years ●S: 19.7 - 21.3 inches (50 - 54 cm); Recommended Age: Children 4 - 8 years ●This bicycle helmet has acquired American CPSC and ASTM safety standards ●Comfortable and Convenient: 360° protective cushion, can be removed and laundered ●Full direction adjustment, head circumference adjuster, side ear adjuster, one touch pack, length adjuster, four adjusters can be adjusted in all directions ●Cooling System11 vents and 6 cooling channels