MOSUL, Iraq - Hasan thought he had seen everything after fighting Islamic State in Fallujah in Tikrit. Then he came to Mosul, and a boy no older then 10 tried to kill him.

"It was utterly shocking," says the 40-year-old soldier, dragging nervously on a cigarette as he remembers the child among a group of young IS suicide bombers.

"I found myself in front of children full of hatred. They all had explosive belts and they were all ready to die. It isn't anything like killing an adult. But we had to do it.

They were all ready to die. It isn't anything like killing an adult. But we had to do it. - Hasan, veteran Iraqi soldier

"It's a cruelty that has no end. For us it is a violent pain - we know we have to fight against children who have been indoctrinated in the name of a sick religion."

This is the reality of war in northern Iraq, where IS is throwing everything - and everyone - at Iraqi forces as they slowly take back Mosul and the surrounding areas in a bitter war that has destroyed the very social fabric of the city.

Children have been spared nothing: poverty, malnutrition and cruelty under IS control; then forced onto the frontlines to be used as spotters, fighters, human shields and suicide bombers as the battles began to rage.

These are tactics that have destroyed family life in the city and its surrounding villages, where IS scooped up youngsters to teach them the ways of their "Caliph".

An Iraqi soldier runs past the corpse of an IS fighter in Mosul (Reuters)

In Hamam al-Alil, south of Mosul, Amir tells Middle East Eye of his own son, Mushak, who swore allegiance aged 11 soon after IS arrived in 2014.

"My children had never gone to school," he said, his face a contortion of fatigue and pain.

"When Daesh arrived my son was a boy full of anger, he could not read or write. They taught him the hatred of the infidels. They taught him to kill.

"In two-and-a-half years he became a soldier of the Islamic police. He wasn't even 14. I tried to stop him swearing allegiance to the Caliph, and he told me: 'Shut up or I'll cut your head'."

"One day he came home with a gun and threatened me - an armed child who comes into the house saying I cannot criticise Daesh - and broke his mother's arm as she begged him to stop."

All villages had recruiters, said Amir, adding that more than half of the children of Hamam al-Alil have been recruited, many of them never seen again.

Amir has lost his son: "I'm not scared he is dead. I do not care. Mushak is the shame of our family.

"Now here everybody hate us, we are desperate, we cannot even go to the shop, we live locked in the house, for fear of being lynched in the street. We lost everything, a son, home, dignity, everything." An Iraqi soldier pauses amid fierce fighting in Mosul (AFP) IS has published dozens of videos of its "young lions" division, children dressed in combat uniform and training for war. In the worst, they have been filmed carrying out executions.

In Mosul, the group are believed to have set up at least one camp for children.

Even those who escape recruitment do not escape the war.

My son now cannot speak, he can only say 'IS is great' - Mosul resident

During an Iraqi advance through al-Shouhadaa in western Mosul last week, the cost on young lives was there to see in every liberated house: dozens of civilians huddling in the dark, waiting for the end to come.

"Daesh used our children as human shields," said one man, Mahmoud, as he embraced a soldier who had stepped into the gloom.

"They entered our house, and forced us to follow them to prevent bombing. My son now cannot speak, he can only say 'IS is great'.

"They wanted him to be a soldier, they taught him maths to count bullets for their magazines, they taught him how to kill someone by cutting his throat. What kind of future do you think he will have?"

Iraqi forces go house to house in Mosul. They often find civilians huddled in the darkness inside (Reuters)

Threats still remain in areas liberated by Iraqi forces.

Ali reopened his clinic in the city's east after Islamic State was kicked two months ago. The hallways stand derelict, the windows were smashed in a car bomb attack that killed Iraqi soldiers in November, but it is at least now providing basic care.

However, the 30-year-old doctor does not feel safe, and not just from the suicide bombers on the roads and drones dropping deadly payloads from the sky. He also fears the children.

He has seen child soldiers enter his clinic and threaten doctors, guessing they were "recruits" from a local orphanage cleared by IS when it was still in control.

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"Daesh certainly recruited them," he said. "Daesh fighters forced all the children and girls to leave the building, and they kept the girls as sex slaves and forced the boys to fight. This generation is a lost generation."

Ali failed to escape from Mosul when IS arrived in 2014, and continued working as a doctor under the rule of Abu Bakr al-Baghdadi. He knows he is now a target - he has seen a lot. Probably too much

"Daesh is still among us. We know who hides them."

But the fear of a child's indoctrinated, immature rage is nothing next to Ali's concern for the future of the lost generation that surrounds him.

A family flees fighting in Mosul (Reuters)

Perhaps 30,000 children have been born in Mosul in two-and-a-half years under IS rule, and none of them has been vaccinated against the terrible diseases that prey on the weak: polio, smallpox, measles to name a few.

Nor do they have official birth certificates - IS documents do not count for Iraqi officials and many civilians chose not to register their children anyway, rendering them effectively stateless.

In Bartella, a town 20km east of Mosul liberated in November, Iraqi authorities have set up a mobile office to give people the choice to request new documents.

Marwa has three children, all without documents. The youngest daughter, Sara, was born after 2014 and her birth was never registered.

My husband and I would never have accepted that Sara had a Daesh birth certificate - Marwa, Iraqi refugee

"My husband and I would never have accepted that Sara had a Daesh birth certificate, but now for us it's all very difficult," she said.

"I come here every day since January and no one gives me any answers. Intelligence officers interrogated me a dozen times, and they verified my family had no links with Daesh, but there's no sign of our documents."

Parents also face a battle to reclaim their identities. Many in Mosul had their Iraqi IDs destroyed by IS, who then issued knew papers. These, in turn, were destroyed when Iraqi forces closed in for fear it would connect them to the group.

Aisha Salman clutched a picture of her son as she waits to submit her application for documents.

He was killed by IS fighters after they found out his father was in the army.

"After my son's death, a Daesh militant stole his documents," she said.

"They stole his life and they stole his identity. Today one of those murderers is defiling the memory of my son. And I do not I know how to get justice."

This article is available in French on Middle East Eye French edition.