By Julie Steenhuysen

CHICAGO, May 7 (Reuters) - About two-thirds of U.S. children will go through a traumatic event in their childhood but few are likely to experience post-traumatic stress disorder, U.S. researchers said on Monday.

The finding reveals a certain emotional resiliency in children, but it also suggests that the way children process troubling experiences is different from adults, said William Copeland of Duke University Medical Center, whose study appeared in the Archives of General Psychiatry.

Copeland and colleagues conducted annual interviews with 1,420 kids at ages 9, 11, and 13 who were representative of the general U.S. population between 1993 and 2000.

By age 16, 68 percent of those studied had experienced at least one traumatic event, such as the violent death of a loved one, physical abuse by a relative, sexual abuse, fire, natural disaster or a serious accident.

"It was a little shocking to me that it was that high," Copeland said in a telephone interview.

Despite those numbers, he said few kids end up developing post traumatic stress disorder, or PTSD, which is characterized by reliving the trauma in some way, avoiding places associated with the trauma and feelings of irritability and being on edge.

About 13.4 percent of those who experienced a traumatic event developed some post-traumatic stress symptoms by age 16, but fewer than 0.5 percent met the criteria for the disorder.

But children exposed to trauma had nearly double the rates of other psychiatric disorders, such as depression, anxiety and conduct problems.

"What it says is kids do fine following trauma, but kids who have problems don't have the types of problems we think they are going to have," Copeland said.

In adults, PTSD usually occurs after a triggering event, such as war, rape, natural disaster or serious illness.

About 6.8 percent of U.S. residents will experience PTSD at some point, according to the Department of Veterans Affairs' National Center for PTSD, which estimates 5.2 million U.S. adults have the disorder in any given year.

The most common at-risk group in adults are those serving in combat.

Copeland said the study suggests clinicians need to look at a wider range of symptoms when evaluating the effects of trauma in children.

"This may be more common than we thought, but it also seems like kids do OK after being exposed to trauma," he said.

"On the other hand, there's a wide range of things we need to keep our eyes on."

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