Child soldier Syria
Children worldwide are used in hostilities as fighters, spies, messengers and sex slavesGetty

Children as young as six years old are being trained as suicide bombers and taken to the front line as blood donors for wounded Islamic State fighters, according to Foreign Policy.

While there are no official figures for child soldiers, human rights groups as well as reporters say that the military training of youngsters is rapidly growing.

U.N. human rights experts have "received confirmed reports of children as young as 12 or 13 undergoing military training organized by ISIL in Mosul," according to a report written jointly by the Office of the U.N. High Commissioner for Human Rights and the human rights office of the U.N. Assistance Mission in Iraq.

Ivan Simonovic, the U.N. assistant secretary-general for human rights, interviewed displaced Iraqis in Baghdad, Dohuk, and Erbil. He said there is a "large and dangerously successful recruitment" program.

Speaking to reporters at the U.N., he said the fighters "appeal" to some of the youngsters and that they have approved adept at "manipulating young men and children." He explained that "they project an image of being victorious".

They impress upon the children the importance of fighting and dying for their faith. and offer the pledge that those who die in the fray will "go straight to heaven."

Not everyone is in favour of children going into battle. "What is striking for me is to meet mothers who [tell us], 'We don't know what to do,'" said Simonovic. "Our sons are volunteering and we can't prevent it."

At the camps, the children who are barely bigger than AK47s, are taught how to fire and load weapons. According to Syria Deeply website, they are shown the best ways to behead someone, using dolls as practice.

The effectiveness of child soldiers as fighters is obviously not as great as adults, so they are used in other ways. Chillingly, they have value as human shields and also to provide blood transfusions for Isis militants, according to Shelly Whitman, the executive director of the Roméo Dallaire Child Soldiers Initiative.

Some of these boys reported that they "were forced to form the front line to shield ISIL fighters during fighting, and that they had been forced to donate blood for treating injured ISIL fighters," according to a report by the Office of the U.N. High Commissioner for Human Rights and the human rights office of the U.N. Assistance Mission in Iraq.

Children are often sold into a kind of modern-day slavery. In Raqqa, where poverty is rampant, Isis persuades parents to send their children to the camps in exchange for money, according to Abu Ibrahim Raqqawi, the pseudonym of a 22-year-old man who lived in Syria until recently. He is the founder of Raqqa is Being Slaughtered Silently, a Twitter account and Facebook page.

Meanwhile, Isis honour their child soldiers killed in battle. A Twitter account run by Islamic militant supporters show a photo of what they say is the youngest soldier to "martyred" for their cause - so far.

The 10-year-old boy is named as Abu Ubaidah. A tweet says that on 9 October he was killed, alongside his father, by an American air strike.