In light of the Colorado shootings, I wanted to share some resources for talking to our children about traumatic events. For the most part, I don't think we should burden them with too much information when they are under school age. But, when they hear about things outside the home, they could need our help.
This is a good article by Peter Levine about talking to children about traumatic events. It's more about personal events, but is helpful nonetheless.
And, a video by Peter describing trauma.
Here's a nice piece from the Child Mind Institute.
And, here's a sweet guide for parents and educators about specifically talking about shootings, etc. Arranged by age.
And, here's a review of the Dark Knight Rises from Commonsense Media; they say it's appropriate for 14-year-olds and older.
Hope this helps in some way.