These helmet toppers are a great way to get kids to actually wear their helmets while they ride their bike. The bunny one is my favorite. What's yours?
http://www.innoprousa.com/helmet_toppers.htm Via Nerd Apporved
The trick would be to figure out how to get them to use the chin strap. Kids usually wear their helmets, it's just that they do it in such a way that they are completely useless.