Currently 21 States and the District of Columbia have laws requiring helmet use by children and five states require helmet use for other wheeled sports (scooters, skateboards and inline skates). Helmet use is significantly higher in places with enforced helmet use laws. There is also evidence that the rate of serious head injury is lower in places where there is greater helmet use. A report from the National Highway and Traffic Safety Administration (NHTSA) reported that 9 out of 10 adults support a law requiring children to wear helmets when cycling and about 60 percent support a helmet law for adults (this number dropped to less than 50% among adults who identified themselves as bicyclists).
The question of why people do not wear helmets is an interesting one and an important one to understand. The following table is from the same NHTSA study.

It seems to me that another reason is that most people do not fully understand the risks involved and the potential consequences of even a minor blow to the head. I also think that many believe that something bad could not happen to them or their loved ones. As a neuropsychologist, I have seen firsthand the devastating consequences of injuries that could have been prevented by helmet use and I am committed to trying to help others understand the need for regular helmet use by adults and children.
My children (8 and 9 years old) understand that they never ride their bikes, scooters or a skateboard without a helmet. My wife and I have reinforced this to the point that we no longer have to remind our children about it. Children will not make these important safety decisions on their own and many will avoid wearing a helmet if they can. It is up to us as adults to reinforce the need to be safe and to set a good example. Children are more likely to wear a helmet if they are riding with others who are wearing them. As parents it is our responsibility to make sure our children have the right safety equipment for all of the activities that they engage in and to make sure they use them.