Harvard Family Research Project has created a resource page on how parents, teachers, and community members can support and communicate with children of all ages during difficult times.
http://www.gse.harvard.edu/~hfrp/advice.html
(Note: On some browsers you may have to scroll down several page lengths before coming to the text.)

The websites listed below to help families talk to their children about the tragedy have been compiled by Reed Martin, J.D. and Connie Mathews.

PBS Kids Resource for Parents.
http://www.pbs.org/americaresponds/parents.html

American Academy of Pediatrics (AAP) offers advice on how to communicate with children and adolescents during times of crisis.
http://www.aap.org/advoacy/releases/disastercomm.htm