Years ago we let a friend's son spend the night after spending the day riding 4 wheelers. He was probably 8 and really pouted when his dad made him wear his helmet. The next day him and my boys went out again, and Caden went off into a shallow ravine and ended up upside down. Broke his ankle but was wearing his helmet. I've never been so thankful that a kid did what his dad said, even when his dad was gone. He's now far from being an angel and his sisters are wild.
We sold our 4 wheeler not too long after that. I didn't trust my boys to follow the rules and that scarred me.