One study focused on Uganda, where an estimated 25,000 children and adolescents have been forcibly recruited into the Lord's Resistance Army, an armed group that began a bloody war against the Ugandan government in 1987.

It found that former child-soldiers who fought with the group exhibited a range of problems long after leaving the battlefield, and that there was little infrastructure in place to deal with the problem. 

Behavioural problems

According to the study, carried out by researchers from the University of Hamburg, almost half the 330 children surveyed had killed someone and more than a quarter had been raped during their time as soldiers.

The researchers found that after leaving the armed forces, a third of the children exhibited signs of post-traumatic stress, more than a third were depressed and over half had behavioural problems.

The figures indicate an urgent need for rehabilitation in the country, the researchers said, pointing out there is just one psychiatrist in Uganda for every 1.3 million people.

The study also found that the overwhelming majority of former child soldiers face continued violence after they return home, with 90 per cent of those surveyed reporting abuse including caning, burning and rape after leaving the military.

Nivi Narang, director of campaigns at the charity War Child UK, which helps 1,400 former child soldiers in Uganda, said that funding was a major problem for many rehabilitation programmes.

"There is just not enough funding," she says. "The kind of funding that is available is just not suitable. We try to get them back into education- it's really important."

Rejected by community

A separate study, carried out in Sierra Leone, found that the extent to which children can recover from the horrors of conflict zones depended largely on the treatment they received after returning home.

Researchers from Harvard University concluded that children who were returned to communities where they were accepted and not isolated from their peers fared better than those who were forced to drop out of school.

"There’s a lot to do in terms of cultural attitudes,"

Nivi Narang, director of campaigns, War Child UK

But the study concluded that children who had been through extremely traumatic episodes exhibited lasting symptoms of psychological disturbance that required far more intensive rehabilitation support.

"Witnessing general war violence, although very common, didn't have a strong effect on the children's psychological and social adjustment over time," said Theresa Betancourt, the child health and human rights expert at Harvard who authored the study.

"In contrast, the effects of experiencing rape and wounding or killing others were longer lasting," she said.

Both studies found that post-conflict support for former child soldiers was severely lacking in the countries it is needed, and warned of "broader consequences for society" as a generation of war-damaged children reach adulthood with such limited support.

It is a concern that has long been recognised by charities working in the field.

"There's a lot to do in terms of cultural attitudes," Narang said. "If children come out and they have no means of getting a job, no means of getting back into education, and are rejected by their families, they will go back to the army.

"It's the only family they know. It's a potential trigger for conflict."

The studies were the first scientific research to focus on the psychological impact of conflict on child soldiers, despite them being used in at least 86 countries around the world.