So I agree with others here that exposing young kids to the ugliness of the world is important. It helps them develop an ability to analyze events and people's attempts to manipulate others. Developing an ability to self-protect is very important part of that process.
The key here is how you define "young kids."
Our DD at 8 made it emphatically clear that she did NOT want to hear any discussion of Sandy Hook. Given her similarity to the victims, it makes perfect sense. Having prior knowledge would probably not help her against an adult with guns coming to her school. Meanwhile, she needs to go to school every day and be able to function, so there's no time for gibbering fear.
Survival mechanism, that. A child lacking in a basic feeling of security is not going to develop in healthy ways. Sheltering them from some of the ugliness in the world is one way we help them develop that sense of security. The removal of that shelter should be gradual to avoid excessive shock.
