I also found this handy guide for buying the right size bicycle:
The following are the typical sizes of bike for the average-size child.
Under 5 years 12ÃƒÂ¢Ã¢â€šÂ¬Ã‚Â or 16ÃƒÂ¢Ã¢â€šÂ¬Ã‚Â wheel
5 to 7 years 20ÃƒÂ¢Ã¢â€šÂ¬Ã‚Â wheel
8 to 10 years 24ÃƒÂ¢Ã¢â€šÂ¬Ã‚Â wheel
11 and over 26ÃƒÂ¢Ã¢â€šÂ¬Ã‚Â or 27ÃƒÂ¢Ã¢â€šÂ¬Ã‚Â wheel
Next time someone tells you to stop actiing like a 5 year old tell them, “I can’t help it. I race BMX.”
Exemptions from the helmet requirement are persons who operate or ride a bicycle (as a driver or a passenger) on a roadway closed to motor traffic; on a trail, route, course, boardwalk, path or area set aside only for the use of bicycles.