Who should wear a bicycle helmet

I saw the weirdest thing yesterday. Two boys were riding their bikes on the sidewalk of one of our major streets (6 lane boulevard). The boy in front had a box of powdered donuts. He was holding the box out and reaching out to give the boy behind some. I watched them for quite a distance ride just like that...one with the box reached out and the other just picking out donut after donut and eating them. They were both wearing those bicycle helmets that people with brain damage wear.