Leader Resources published a very helpful article on "Talking with Children after Tragedy" with all kinds of resources after the shooting in New Town, CT. Please take a look at these excellent tips on talking with younger and older children and teens. There are also many links to further resources.
Episcopal Relief & Development has put together lessons for all ages for the time after a disaster. This was primarily written for use after deadly natural disasters, but the effects of fear and trauma can be the same. The lessons are written in a way that they could be useful no matter what frightening event has occurred and contain good information and tips for working with the specific age group. There are three complete lessons for different ages: Ministering to Children After a Disaster, Resources for Grades K-5, Ministering to Youth After a Disaster, Resources for Grades 6-8, and finally Ministering to Teens After a Disaster, Resources for Grades 9-12. There is also a lesson available for adults.
The Episcopal Diocese of North Carolina created a very good page of Resources for Helping Youth (and children) Respond to Tragedies. The first piece is a set of guided questions for parents when talking with their child. Also, helpful links have been added by topic.
Peace I leave with you; my peace I give you. I do not give to you as the world gives. Do not let your hearts be troubled and do not be afraid. John 14:27