http://www.chp.ca.gov/html/bicycleriding.html
http://www.chp.ca.gov/html/skateboard.html
Please note that anyone under 18 who uses a skateboard, non-motorized scooter, rollerblades or roller skates is required to wear a helmet. For bicycle riders, a person under 18 years of age cannot operate a bicycle or ride as a passenger without a properly fitted and fastened bicycle helmet that meets the standards of the American National Standards Institute (ANSI) or the SNELL Standards for Protective Headgear.