Up to 400 abducted Yazidi children are reportedly being trained as potential suicide bombers by Isis.
Kurdish authorities told CNN they had evidence 600 children were kidnapped from Iraq's Sinjar province and the surrounding Yazidi villages, but that 200 had managed to escape.
The news channel reported there were now fears Isis was using them to bolster its numbers after it came under pressure following the recapture of Ramadi by Iraqi forces at the end of last year.
It said Isis had put its most experienced fighters on the front lines and was using child soldiers to plug the resulting gaps in sentry positions and its suicide bomb squads.
A 12-year-old boy who escaped the group’s clutches told CNN he had been trained by the group to be a suicide bomber.
He said: "There were 60 of us. The scariest times for us all were when the airstrikes happened. They'd lead all of us underground into the tunnels to hide.
“They told us the Americans, the unbelievers, were trying to kill us but they, the fighters, they loved us. They would look after us better than our parents.
"When they were training us they would tell us our parents were unbelievers and that our first job was to go back to kill them."
He said the youngest boy in the camp was just five years old and that they were dubbed “cubs of the caliphate” by their trainers.
The Syrian Observatory for Human Rights told the Independent there had been 29 suicide attacks carried out by child suicide bombers in Syria over the past four months - but stressed they were not all necessarily Yazidi children.
During the Sinjar massacre in August 2014, an estimated 5,000 Yazidi men were murdered and thousands of women were kidnapped to be forced into sex slavery.
Yazidis are a small monotheistic religious group who mostly live in Iraq. They believe there is one God who created the world and placed it under the control of seven angels - the chief of whom is the Peacock Angel, Melek Taus.
But Isis regard them as devil worshippers and have attempted to eradicate the sect. There are an estimated 50,000 displaced Yazidis in refugee camps in the Middle East and Europe.
Rob Williams, the CEO of child soldier charity War Child UK told the Independent Isis' use of children "equated to child abuse".
He said: "Children have the right to safety, protection and education.
"That IS has deliberately taken children into an area where they are likely to be required to fight, exposed to atrocities and physical danger and denied an education (particularly girls) is not in a child’s best interests and equates to child abuse."
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