Post Traumatic Stress Disorder
http://www.aacap.org/publications/factsfam/ptsd70.htm
A child or adolescent who experiences a catastrophic event may develop ongoing difficulties known as posttraumatic stress disorder (PTSD).
This fact sheet from the American Academy of Child and Adolescent Psychiatry can provide additional background on PTSD.
What is Post Traumatic Stress Disorder
http://www.nimh.nih.gov/HealthInformation/ptsdmenu.cfm
This article from the National Institute of Mental Health offers information on PTSD which is a kind of anxiety disorder.