Former Islamic State (ISIS) child soldiers who managed to escape have come out to reveal their harrowing life inside ISIS camps, the Daily Mail reported.

The young boys said they were snatched from their families and ordered to undergo rigorous training as child soldiers. Those who refused to join were subjected to brutal punishments, they said.

They said one 11-year-old boy, known only as Nouri, had one of his legs broken after he refused to become a "cub of the caliphate."

The children said they were taught ISIS' radical brand of Islam and ordered to kill even their own parents.

One former child soldier said they were not even allowed to cry by their ISIS instructors.

"We weren't allowed to cry but I would think about my mother, think about her worrying about me and I'd try and cry quietly," he said, according to the Daily Mail.

"When we escaped and I saw my mother again, it was like coming back to life," the young boy said.

Some of the former ISIS child soldiers are now living in the refugee camps in northern Iraq. Their families said the repeated beatings and endless propaganda taught them have caused them to wake up in the middle of the night with nightmares while others suffer from seizures.

Those who were unable to escape were ordered to wear explosive vests and sent to the frontline to fight ISIS' enemies, the escapees said.

A Kurdish commander attested to this, saying his men frequently come face to face with these young ISIS fighters.

Aziz Abdullah Hadur said "many times when we are facing ISIS, we see the children at the front line and they're wearing explosive vests. They are brainwashed," he told CNN.

"When they make it through our lines they kill our fighters. It's an unbelievably hard decision.You don't know what to do because if you don't kill them they'll kill you," he said.

Pictures of young beardless ISIS suicide bombers have become a common sight on social media as ISIS continues to recruit children as soldiers. Analysts say this is an indication that the jihadist organisation is finding it increasingly difficult to replace its fighters who have been slain in battles or who have defected to enemy forces.