1.Toddler helmet compatible head circumference: (48cm-52cm / 18.9"-21") for 3 and older kids.Note:Please according to head circumference to choose. 2.7 pieces toddler helmet and knee pads:Helmet /2 Elbow pads/2 knee pads and 2 wrist guards ,7pcs Protective Gear set, bring you all-round and perfect protection while doing sports. 3.Childrens protective gear Materials:knee protection for skating,bike and other multi sport,Made of premium ABS ,breathable sponge, not only are breathable comfortable ,but also protective, perfect gift for kids. 4.knee pads for kids: Multiple adjustable elastic straps and velcro closures fit for various knee circumference. 5.Compatible sports scooter helmets for kids: This outdoor sports protective gear set fit many different outdoor sports,such as scooter, skateboard, bicycle, roller,high protective for your kids.