When the new Diagnostic and Statistical Manual of Mental Disorders, DSM-5, is published in May, a small section could alter the lives of millions of children.
The manual, a reference bible for psychiatrists around the globe, will include pioneering guidelines to help doctors diagnose post-traumatic stress disorder, or PTSD, in children under the age of 6, according to two psychiatrists who worked on the draft.
"When the DSM was written 20 years ago, it was mainly written about adults and field trials were all about adults," said Dr. Charles Zeanah Jr., vice chairman of Child and Adolescent Psychiatry at Tulane University. "The problem was there were children who were very severely traumatized but didn't meet criteria because they weren't included in the studies. Nobody knew what it looked like."
But new research details what PTSD looks like in young children and finds that treatment for these young sufferers can be effective, he said.
The addition of a developmental subtype for any disorder is a first for the manual, which makes the expansion of the PTSD entry so exciting to researchers.
"This is just what I hope will be the beginning of thinking of how different disorders manifest at different points in the life span," he said. "For depression, say, we're not as clear about what the developmental differences ought to be."
Small children develop PTSD at the same rate as adults -- one in four -- and the number of potential sufferers is vast, said Dr. Judith Cohen, a psychiatry professor at Drexel University's College of Medicine.
Consider sexual abuse cases alone: A quarter of all girls and a sixth of all boys have been sexually abused, and about a third of those are preschool-age, she said.
"If we're talking about 25 percent [who] have PTSD, we're talking about a lot of children," Cohen told ABCNews.com. "I think [the DSM change] is going to be a huge contribution to early identification and early prevention of negative outcomes for young children."
And yet because existing DSM criteria doesn't apply to young children, and because of society's tendency to idealize children as resilient, pre-schoolers aren't getting the diagnoses they desperately need, Zeanah said.
Cohen agreed: "The younger the child, the less likely to capture PTSD."
If untreated, exposure to severe trauma in a child or adult can result in devastating health effects, including a permanently altered brain, heart disease and suicide risk that is six times higher than average, said Cohen, who is also the medical director at the Center for Traumatic Stress in Children and Adolescents in the West Penn Allegheny Health System.
Classic PTSD symptoms, in both adults and children, include "re-experiencing" (nightmares, flashbacks), avoidance (trying not to think about the trauma) and hyper-arousal (jumpiness, trouble sleeping), Cohen said.
But young children express symptoms differently.
"Adults might say, 'It's like I'm watching a movie," Zeanah said. "A 2-year-old will repeatedly play out scenes that are aspects of the traumatic experience, often in an agitated and frightened way."
Existing criteria for PTSD aren't appropriate for children, no matter how bright or verbally expressive a young child may be, she said.
"The problem with very young children is they can't adequately describe their internal state," she said. "A child who's 3 or 5, they'll be like, 'Mommy, what does 'ashamed' mean?"