I believe here in Clark County in Warshingtown state the law says anyone under 18 must have a helmet when biking, skateboarding, or rollerblading. Now, with all the 13yr old kids riding BMX's down the wrong side of the street, I can't remember the last time I saw one WITH a helmet. I've also seen groups of helmetless kids riding all willy-nilly over the road and a cop roll by the opposite direction, without so much as a passing glance. So if your state is anything like this I wouldn't worry about it.