"Nasir" is one of the lucky ones. He managed to escape from the grasp of ISIS, which was training him to be a suicide bomber. He is just 12 years old.

The boy is now reunited with his mother at the Esyan refugee camp in Kurdistan, home to almost 15,000 Yazidis fleeing ISIS. He's asked CNN not to broadcast his face or voice, or to disclose his real name.

"There were 60 of us," Nasir says. "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."

The use by ISIS of child soldiers has been well documented. Last week, for example, a new propaganda video was released featuring an English-speaking child. But the reality behind the headlines is even more horrifying.