In 2009 around 2 million children in the U.S. had a parent in either the active or reserve component of the military. A study of some of these children by researchers from the RAND corporation found that across all age groups children from military families reported significantly higher levels of emotional difficulties with a third reporting symptoms of anxiety. Older children had more difficulties with school and more problem behaviour such as fighting while younger children had more anxiety. Girls had fewer problems in school and with friends but also felt more anxiety. The impact of a longer deployment was more marked on girls - perhaps because they were more likely to take on extra chores - while the mental health of the parent remaining at home was also an important factor. There were no significant differences between the children in terms of which service their parents were in.

You can find out more about this research at

http://psychcentral.com/news/2009/12/08/emotional-challenges-as-deployment-lengthens/10048.html