More than 31,000 pregnant women living in the so-called Islamic State are being used to create the next generation of terrorists, a wide-ranging report that details how the terror group indoctrinates children has revealed.

In a report called Children of Islamic State, the London counter-extremism think-tank Quilliam has released results of an investigation into how Isis recruits children and trains them for jihad through indoctrination both at home and in school.

The report, which has been endorsed by the UN, states that Isis regards children as better and more lethal fighters than adults. Rather than being converted into radical ideologies, they are a "blank slate" which allows them to have extreme values indoctrinated from birth. Techniques to normalise brutality include encouraging children to play football with decapitated heads.

Researchers said that boys learn from a rigid Isis curriculum, churning out memorised verses of the Quran and attending ‘Jihadist training’ – which involves shooting, martial arts and weaponry. Girls, however, are known as the ‘pearls of the caliphate’ and must remain veiled, hidden, confined to the home, and taught to look after husbands.

Nikita Malik, a senior researcher at Quilliam, told The Independent: “There’s a systematic creation of the next generation of mujahideen – the next generation of fighters.”

She added that the fact that 31,000 women are now pregnant “shows it’s not being done randomly in any way, this is a very long-term preparation for these children to grow up with severe religious, theological and national indoctrination.”

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She said: “What we found very interesting was the reasons why this army is being created. Firstly, children are a completely blank slate and so don’t have the cognitive abilities or the adult decision-making processes, so they can be manipulated because they are vulnerable to do all kinds of things.

“The families play a key role in doing this as well. Mothers play a key role: they read story books on martyrdom to their children at night. The families are teaching them what is right and wrong. This purity angle is very interesting.”

“This is one of the gravest situations on earth. Children are the key to the future. Indoctrination in Islamic State begins at birth, and increases in schools and training camps,"

Noman Benotman, President of Quilliam, added: “This is one of the gravest situations on earth. Children are the key to the future. Indoctrination in Islamic State begins at birth, and increases in schools and training camps. Children are instructed in a particular interpretation of shari’a, desensitised to violence, and learn specific skills to take up the banner of jihad.”

The extraordinary report on children in the 'caliphate' adds that from August 2015 to February 2016, 254 instances of children being used in Isis propaganda were recorded. In the last six months, such material has depicted 12 child executioners, with one participating in a public execution.

Inside Isis secret tunnels Show all 7 1 /7 Inside Isis secret tunnels Inside Isis secret tunnels Network of underground tunnels was discovered by Kurdish forces after they regained the town of Sinjar in Iraq Inside Isis secret tunnels A member of the Peshmerga forces inspects a tunnel used by Isis militants in the town of Sinjar, Iraq Reuters Inside Isis secret tunnels An entrance to the tunnel used by Islamic State militants is seen in the town of Sinjar, Iraq Inside Isis secret tunnels The secret tunnels allowed militants to freely move underground Inside Isis secret tunnels The tunnels appear to be wired with electricity Inside Isis secret tunnels Some of the tunnels are 30 feet deep Inside Isis secret tunnels Concerns remain that parts of the tunnels are rigged with explosives

Details of the so-called Islamic State’s treatment of women has been well documented by the United Nations Assistance Mission in the region. In January, it claimed those being held as slaves by Isis are “predominately women and children and come primarily from the Yezidi community”.

The UN said it was able to verify reports that, on 21 June last year, between 800 and 900 children were rounded up in Mosul and abducted for military training. It said it had also been informed that those who refused Isis commands were flogged, tortured or raped.