I coach high school sailing in Boston and the helmet issue has been a major point of discussion at the last couple league meetings. Many schools are making helmets mandatory for their sailors because they have been losing one or two players to concussions every season. I think with the current attention TBIs are getting in football, hockey, etc. we are going to see a strong movement towards helmets in Jr. Sailing.
At MIT, Fran (sailing master) is also very concerned about the head injuries and has bought helmets for his sailors. They are optional to wear, and Fran is also trying to solve the problem by switching to carbon booms on the FJs and raising the gooseneck. We've also gone to Gnav vangs to eliminate extra purchases flying across the ****.
In general, I have found kids are more likely to get hit in light air when they aren't paying attention, than in heavy breeze when they gybe with a hand on the vang, etc.