Met Elfo The defacto design standard for your child's first bicycle helmet, Met's Elfo has been built to exacting standards & carefully formed to offer the best protection, as appropriate for small children. Quite right too. Unlike an adult helmet, the Elfo & it's bigger sibling the Genio are shaped to suit the needs of the smaller wearer, with a flat rear section for when they are riding in a child seat, cavities in the shell where it meets the vulnerable fontinella on top of the child's skull & a anti-pinch strap & buckle arrangement. So, it's safer than most other kids lids & has cooling vents with an insect net to keep bugs & stuff out, so you're happy, & the nice variatin of colours available means there should be something to suit every child's taste, so they're happy. Everyone's happy. Adjustable fit suit head sizes from 46 to 53c. Measure the head circumference horizontally at the widest point, just above the ears.