For Aleppo's children "blood has become like water". Filmmaker Marcel Mettelsiefen has spent several weeks meeting children facing unimaginable horror as they work in a city hospital.

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Twelve-year-old Mohamed Asaf's days are filled treating Aleppo's war wounded. He starts work at 8am and usually gets to bed by 11pm.

When filmmaker Marcel Mettelsiefen meets him in the city's Dar al-Shifa clinic, Mohamed is battling to save a young girl's life.

After months bearing witness to the human tragedy of Syria's civil war, he has become desensitised to the horrors: "With time it has become easy: blood has become like water to me," he says.

"In the beginning, when I saw blood, I would shiver and be frightened but now I see blood as water I don't have any problem when I see it."

Mohammed is just one of many children in Aleppo growing old before their time. Another young medic, Yussef Mohamed, tenderly cares for an injured fighter from the Free Syrian Army. Their worlds have been turned upside down: in Aleppo, adults are being cared for by children.

Before Aleppo entered the revolution this city had 5,000 medical staff. Now 600,000 civilians are cared for by just 30 doctors and nurses, along with the help of children like Yussef and Mohamed.

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A scarred city

Aleppo is a broken city. People fish the river Queiq for bodies. It used to be sacred but not anymore. A hundred and ninety bodies have been recovered from the water so far, some with their hands tied behind their backs.

The dead are buried in a playground - the gravediggers do their work in the shadow of a children's game of football. A makeshift office is set up to identify the victims.

There is no running water in Aleppo, no electricity and food is far from plentiful. With little government or international aid getting through there is a void to fill and hard-line Islamist group Al Nusra is on hand to help. Their aid vans patrol the streets handing out clothing and food. It is a PR opportunity and a chance for them to win hearts and minds of the people.

For the people in Aleppo have much to fear. Three days after we filmed 11-year-old Yussef Mohamed treating an injured soldier he was killed by a government shell. Another young victim of Syria's descent into civil war.

This film above was shot by Marcel Mettelsiefen, produced/directed by Teresa Smith and edited by Agnieszka Liggett.