CONSTRUCTION - ABS Hard Plastic Shell with EPS Liner. ACTION FIT - Designed for street and skate helmets, this streamlined fit system offers an adjustable, secure fit with the turn of a dial. SPECIFICATIONS - X-Small (49-53 cm) and Small (51-55 cm) Sizes. Important: always take a measurement. Sizes and shapes can vary, even within an age range. Using a helmet that does not fit can be dangerous; 10 Vents. The bright colors and popping patterns of the Bell Kids' Span Helmet make staying protected exponentially more fun. Add in an adjustment system that mirrors the one found in adult-sized helmets, and you've got an ideal blend of comfort and style that'll have your kid reaching for this helmet before you even have to mention it. For summer days, 10 vents across the helmet usher in cooling airflow for additional comfort and motivation to keep riding in helmet-clad safety.