The best free video anybody has yet produced for "tweenagers" from about 8 to 12. Preaching, but all done by kids. Damaged helmets, jello and egg smashes, good fitting instructions and a few seconds on rules of the road. The discussion of brain injury doesn't quite match the brain-injured kid in Jello in a Jar, but this video is well worth showing to a class. Nine minutes. Free from the US Dept of Transportation. Go down their page to "Topic" and click on the gray arrow to drop down the list of topics. Click on Bicycle Safety, then click on the gray Submit Topic button. They have general bike safety videos as well.

http://www.nhtsa.gov/people/outreach/media/catalog/Index.cfm

In case this looks familiar to some, or you want to see the threads,
here is this offer from SD archives:
http://archive.slickdeals.net/showthread.php?sduid=84772&t=201421
http://archive.slickdeals.net/showthread.php?sduid=84772&t=121375