IMO, for what is worth, a helmet should be atop any head that is on something with wheels or legs (bike, ATV, skate board, roller blades, motorcycle, horse, etc). As was pointed out you never know when in a blink of an eye you will be involved in an accident. When I started riding back in the early 80's I visited a local bike shop to buy some goodies for the bike my brother had sold me for $12. The shop guy asked if I had picked out a helmet to which I replied no. He told me you can wreck your bike and replace it or just about anything on it but if your wreck your brain there is no replacement. I picked up a helmet that day and have never been on my bike without it perched proudly atop my head.

Last year one of our students (I teach in a middle school) was riding her ATV, a group of boys passed in going in the opposite direction on their ATV, she turned around to see who went by took her eyes off the road for just a second but it was long enough to change her life forever. Her ATV went down an embankment hit a rock she became airborne and smashed her unprotected head into a tree. She is now in a wheelchair, has trouble communicating and is one very sad young lady. Sadly, as we talked with our classes after the accident few if any saw a helmet as the most important thing they should own and use if riding a horse, an ATV, a bike, skateboard, etc. They feel they are immune to the same tragedy. I only wish they would open their eyes to the reality of the situation. Their classmate is a daily reminder of what can and does happen.