Anything that protects the skull, at any age, makes a difference. Children are vulnerable because they don't have the develpment of spatial awareness and balance that adults posess, plus a lack of awareness of danger from other road users etc. Damage to the skull caused by falling onto concrete - a normal cycler's surface - can be fatal, so any cushioning of an impact has to increase survival, and limit potential brain damage. Helmets for all cyclist have to be a sensible option.