(McClatchy-Tribune Information Services) -- When Amiyah Martinson's father left Thursday on the guided-missile frigate Nicholas, it was the third deployment the 6-year-old Virginia Beach girl had experienced.

She put up a brave front until the ship pulled away, heading toward Africa. Then she cried. "She holds it in until she can't anymore," said her mother, Shelly Martinson.

So it did not come as a surprise to Martinson that children from military families -- especially those with parents on long or repeated deployments -- experience higher levels of anxiety than children in the general population.

Still, a study released today by the journal Pediatrics put some numbers on the issue by interviewing 1,500 children from five branches of the military. Their non-deployed parents or caregivers were also surveyed.

The "Children on the Homefront" study found that one-third of the youngsters had emotional difficulties. Girls struggle more than boys during deployments and the period when the parent returns. Older kids are more likely to have difficulties at school and with fighting, while younger children instead tend to exhibit anxiety.

According to the children's caregivers, the longer a parent was deployed in the last three years, the harder time the children had. Children who lived in military housing fared better than those in families who rented homes in the community.

Children whose main caregiver has emotional difficulties were more likely to have more problems as well. Joyce Razer, executive director of the National Military Family Association, uses the adage "If Mama's not happy, ain't nobody happy" to describe that finding.

The study was conducted by RAND , a nonprofit research organization, for the National Military Family Association, which is based in Northern Virginia. Razer said the organization wants to track the effect of deployments on military children with an eye toward developing services to help families at home. She said this is the largest study to date to examine how military children and spouses fare on social, academic and emotional fronts.

The study's release is particularly pertinent as the country prepares to send more troops to Afghanistan. The study will follow the children over time, so more data are expected.

Children ages 11 to 17 were interviewed between June and August 2008. The children were drawn from those who had applied for Operation Purple camps, which the association provides for free to military children at sites across the country.

The study's authors outlined several limitations of the study. One, families who applied for the camp might be more, or less, stressed than other military families. Also, the comparative sample base of children from the general public, which showed 9 to 15 percent of 7- to 11-year-olds as having anxiety, were from 2001 studies, which might have changed since then.

The symptoms and behaviors were also self-reported or assessed by caregivers who are not trained specialists.

Still, people close to the subject said the findings ring true. Nancy Wiley is regional programs director for the Armed Services YMCA of Hampton Roads, which has programs designed to help children and non deployed caregivers deal with emotions and hardships during deployments and after military parents return.

She has noticed that it's particularly hard for children who have a close relationship with the deployed parent. Also, "w hen mom or dad returns, there's a period of adjustment when there's a new discipline system. That can be difficult sometimes."

Betsy Murdock, director of clinical counseling at Catholic Charities of Eastern Virginia, said boys are more apt to act out aggressively and girls often internalize their feelings, which aligns with the study's findings.

She said media coverage of wartime events also adds to anxiety when children see the potential for the parent to be harmed.

Martinson, 34, said she notices her older daughter, Amiyah, hiding her feelings more than her 4-year-old, Breanna. Their father, Nathan, took them each out on dates before he left last week. They each have "Daddy dolls" with his photo on them and Build-A-Bears with his recorded voice. He also made video recordings of himself they can watch.

Martinson said the Armed Services YMCA -- which assists military families with recreation, child care and other programs -- has been a godsend. She also appreciates the counselor at Amiyah's elementary school, who talks with her regularly about her father's deployment.

She said Amiyah sometimes will misbehave at school during her father's deployments.

"I'd ask her about it and she'd say she was upset, and it would come down to she wanted her dad. I told her, 'You need to say that.'"

Copyright (C) 2009, The Virginian-Pilot, Norfolk, Va.