What size helmet should your 9 year old wear?

Answer 1

There is no age standard for helmet sizes, A helmet is sized according to the circumference of the persons head. Taking a tailors tape measure, measure from the tip of one ear back to the tip of the ear, Then determine which helmet feels comfortable to the shape of the persons head, Make sure it's comfortable and does not move front to back or side to side. Listed below is a link to the size chart from the Bicycle Helmet Safety Institute.

Answer 2

I think a size 158. Ten year olds have big heads.