In the report, it said that young boys are being used by armed groups as porters and human shields at the front lines. It added that some girls are being married off early to protect them from a widely perceived threat of sexual violence. Both sides of the conflict in Syria have accused each other of using children to protect themselves.
"The majority of people who are raped in war are usually children and that probably is the case in Syria," said Forsyth. He added that they don't have exact numbers but "I have interviewed children who were sexually harassed."
The report says that combined with the breakdown of society in parts of the country, and more than 3 million people internally displaced, the conflict has led to "the collapse of childhood for millions of youngsters."
The number of U.N.-registered refugees topped 1 million — half of them children — earlier this month.
Mohammed, the Beirut supermarket employee, stopped going to school after it closed because of the fighting. As the eldest of three siblings, he was sent by his family to Beirut to stay with his maternal uncle, hoping he could find work to help sustain the family.
"I make about 15,000 pounds ($10) a day," said the portly boy from the northeastern village of Shadadeh in Hassakeh province, which witnessed heavy clashes last month forcing thousands of its residents to flee.
"If I don't send money to my family, they won't be able to buy anything," he said. Mohammed gave only his first name, fearing for his security.
At a Beirut gas station, Suleiman, a teenager wearing a T-shirt and a blue baseball cap, spends his day washing cars.
"The fighting and shelling were terrifying in my city," said the boy from the oil-rich eastern city of Deir el-Zour near the border with Iraq — an area that sees almost daily fighting between troops and rebels.
Forsyth said even though children are by nature resilient, the trauma they have been through will have a long-term impact on their lives.
"For millions of Syrian children, the innocence of childhood has been replaced by the cruel realities of trying to survive this vicious war."
Bassem Mroue can be reached at www.twitter.com/bmroue
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