Size XS - Suggest for infant/toddler 0-2 years old Size S - Suggest for kids 3-6 years old Size M/L - Suggest for kids/Teens over 5 years old Dual Certificate - US standard CPSC 1203 & ASTM 1447 verified. Comfort and Convenience -360° inner pads and removable and washable. Adjustment System - With dial turn ring, easily to adjust head range. Cooling System - 11 air vents & 6 cooling channels No Risk To Buy : If you have any problems or questions, please connect us, we are committed to providing better products and services to children and parents. Toddler Bike Helmet for Boys and Girls, Adjustable Kids Helmets from Infant/Baby to Children, 1/2/3/4/5/6/7/8 Years Old