Helmet has 11 breathable vents for airflow to keep user cool. Chin straps and velcro are easy to adjust. The adjustable straps and nylon button could be flexible to different sizes of knee elbow and wrist the knee pads elbow pads with wrist guards could offer custom flexibility according to the user desire. Manufacturered by LIANGZHILIAN. This outdoor sports protective gear set fit many different outdoor sportssuch as scooter skateboard bicycle rollerhigh protective for your kids. Before you use the helmet please untie the buttons that connect the straps on both sides of the helmet. Depending on the size of your head rotate the red adjustable knob on the back of the helmet and attach the button in the middle of the strap. Helmet compatible head circumference: (50cm-54cm / 19.7"-21.2") for 3 to 7 years old kids. Suitable for 15-35 kg the kids.Note: Please according to head circumference to choose.