One of the men raised his sword and hacked off Sami’s head.

“They told us to learn like this. This is the way to cut people's heads off,” Hussein says.

“The girls were crying on his body. And I thought, 'My poor friend'. We took his body. One of my friends carried his head and I carried his body. We threw him on the garbage pile.”

Like 38,000 others, Hussein now lives in the massive Khazer displaced person’s camp near Mosul, one of more than a dozen camps set up to deal with the crisis.

On the day we visit, Hussein is with his family and safe from harm. He’s playing a robust game of catch with a soccer ball and some rowdy friends. It’s impossible to tell what’s going on inside his head. But for today at least, this young boy seems to be coping.

Almost half the people who live here are children. Almost all have seen things a child should not see.

In Save the Children's “psycho-social first aid” space at Jada’ah camp near the city of Qayyarah, Luma* edges shyly up to us. She speaks in a whisper but this is a story she really wants to tell. It's about how she tried to escape IS with her mother and little sister.

When IS discovered them leaving, they knocked her mother to the ground and then shot her dead in front of her daughters. Luma, who was 12, adopted her mother’s role. She picked up her 18-month-old sister and carried her for two hours until they reached a checkpoint – and safety.

Sabeen*, 10, is next. Her nose is scarred, her eyes sad. She walked out her front door one day to go to school when a car bomb exploded nearby. It’s hard to imagine the noise. Shrapnel killed her brother and carved new lines across her face.