Syrian refugee children are paying a cruel price as civil war rips their country apart, the United Nations warned Friday in a report with heart-rending testimony from youngsteriven from their homes.

"This is impossible to forget. It's like someone has stabbed me with a knife when I remember," 15-year-old Taha, who saw seven corpses near his house in Syria, told interviewers with the UN refugee agency (UNHCR).

He and scores of other Syrian refugee children in Jordan and Lebanon were interviewed for a 60-page UNHCR report, starkly laying out the trauma of young exiles from a conflict that has killed over 120,000 people.

The children's last names were not revealed, to protect them and their families.

"It is important that this human face of the refugee crisis is not forgotten," Volker Turk, UNHCR head of international protection, told journalists in Geneva.

"And if you look at what children face, they illustrate very strongly what this crisis is all about," he said.

Children make up around half of the more than 2.2 million Syrians who have fled their homeland, according to UN numbers of registered refugees.

Syria's neighbours meanwhile estimate some three million Syrians have already left the war-ravaged country, which means around 1.5 million Syrian children are living as refugees.

"Looking back over the last 20 years, the Syria refugee crisis for us is unparallelled since the Rwanda crisis," Turk said, referring to the 1994 genocide in the African nation.

He pointed out that children also represent about half of the 6.5 million people driven from their homes but who remain inside Syria.

'Blood up to people's knees'

In the report, the children describe in words and with drawings the horrors they have witnessed and the turmoil within.

"There is blood up to people's knees in Syria," said 17-year-old Sala.

And 16-year-old Maher, who was tortured in Syria and whose father remains missing there, said: "My first wish would be to go back to Syria and to have my father released."

Some of the children also drew pictures of weapons of war and bodies.

"The idea of home and warmth is gone with a stroke," said Turk.

"There is a lot of psychological scarring and a lot of trauma... You see it in sleeplessness, children being very withdrawn, there is stuttering, bed-wetting."

Anger was also common, with some boys wanting to return to Syria to fight.

Other scars are physical: 741 Syrian children were treated for war wounds in Lebanon in the first six months of this year, and 1,000 cared for in the vast Za'atari refugee camp in Jordan.

The massive influx of Syrians has stretched food, water, healthcare and accommodation resources to the limit in the host countries, and also overwhelmed their education systems.

In Lebanon, for instance, the number of Syrian youngsters equals the 300,000 local children in state education -- another 700,000 Lebanese children are in private schools.

Fewer than half of Syrian refugee children in Lebanon are receiving a formal education.

In addition to concerns about transportation costs, or the need to take jobs to support their families, Turk said around a third of the children interviewed by UNHCR hardly ever leave their temporary homes, in part due to the anxiety of being in a strange environment.

"There's a virulent mix of distress amongst children, the access issue to schools, but the economic pressures as well, that are all combining to mean that lots of children are not in school and not in that normalising environment," said UNHCR spokesman Adrian Edwards.

Many Syrian refugee children are growing up in fractured families, and are often the household's primary breadwinners, UNHCR said.

Over 70,000 Syrian refugee families live without fathers and over 3,700 refugee children are either unaccompanied by or separated from both parents, it said.