The only people that don't need helmets -- are the ones with nothing to protect. OK enough with the clichés. Wearing a helmet doubles a kid’s chance of avoiding serious head injury when in an accident involving the head. I once saw my 4 year old fly into a rock going about 20. The rock stopped her bike, and then she flew head-first into another rock. Everyone was shocked, then relieved when after a moment of no movement she jumped up and said "I not hurt!" as if to comfort us. Since then she has learned how to use the brakes.