Bell Marvel - Casco de bicicleta para niños y adultos. --. Acerca del producto: Fits head sizes: 50-54 cm. True fit self-adjusts for a proper fit everytime. High-impact reflectors for visibility. 12 vents keep heads extra cool. Pinch guard ensures pinch-free buckling and built-in visor. **Always take a head measurement. Head sizes and shapes vary even within an age range. Using a helmet that does not fit can be dangerous.