Mini Hornit Helmets The coolest kids’ bike helmets around, the Mini Hornit Lids feature stylish and fun designs so kids actually want to wear them! Fully adjustable, super comfortable and lightweight, the Mini Hornit Lids have an integrated rear facing LED for additional safety in low light conditions. The most common circumference of children aged 2 to 4 years is 51 to 53 cm. A children's bicycle helmet in size 48 to 52 cm is therefore an excellent choice for most children in this age group. For children from about 4 years old you should probably look for a helmet with a circumference greater than 53 cm.• Head adjuster • 11 air vents • Complies with AS/NZS 2063:2008 • Small: 48-53cm • Medium: 53-58cm LED Light • 3 modes • 2 x AG3 cell batteries • 10 hours constant • 20 hours flashing