Extremism experts warn children are being indoctrinated and radicalised from birth, leading to a 'whole generation who will know nothing other than ISIS ideology'.
Their comments follow the release of a sickening new video that purports to show a boy of about 10 years old shooting dead of a 19-year-old Israeli-Arab who was taken hostage by the terror group, Mail Online reports.
The footage appears to show the child, now believed to be a French citizen, raise his gun and aim it at Muhammad Said Ismail Musallam's forehead before shooting him at point blank range.
The footage of a child seemingly carrying out such a brutal execution has sent shock waves around the world, but it came as no surprise to experts who have been following the brainwashing of youngsters by ISIS.
Charlie Winter, a researcher at the Quilliam Foundation, a counter-extremism think tank, said: ‘It is something that has been going on for a long time now.
He said: ‘This is going to be a long-term problem – there is going to be a whole generation of kids in Northern Iraq and Eastern Syria who will know nothing other than Islamic State ideology.
Videos released by the group reveal the tough military training children are forced to undergo and the warped curriculum they learn in terrorist-run schools.
Last month, ISIS released a slickly-edited propaganda video showing boys as young as five being indoctrinated at a military-style training camp for 'cubs' in Syria.
I don’t think there is a choice in it for the children – they are the biggest victims in all of this Charlie Winter, Quilliam Foundation researcher.
Children are said to be taught how to use weapons and even show how to behead using dolls.'They teach them how to use AK-47s,' an Iraqi security official told NBC News.
'They use dolls to teach them how to behead people, then they make them watch a beheading, and sometimes they force them to carry the heads in order to cast the fear away from their hearts.'
Other footage shows children being taught in an ISIS school before learning hand-to-hand combat and how to fire a gun.
Pictures posted on ISIS-linked social media accounts have included babies posing with firearms and young children holding up the heads of beheading victims.
Some propaganda videos attempt to show the 'lighter' side of life under the control of the caliphate, and unsophisticated ploys such as giving sweets to children seem to have played a part in the radicalisation.
Human Rights Watch, an organisation which defends the rights of people worldwide, interviewed four former ISIS child and adult fighters, as well as civilians in the terrorist-controlled areas in Syria.
It found the militants have actively recruited children to send to military training camps and have used them in operations including suicide bombings.
In November last year, a United Nations Commission of Inquiry on Syria report found that massacres, the beheading of boys as young as 15, and amputations and lashings in public squares with residents - including children - forced to watch were on the list of crimes.
The report found ISIS was trying to indoctrinate minority children and turn them against their families.
Speaking to MailOnline, Professor Anthony Glees, director of the Centre for Security and Intelligence Studies at the University of Buckingham, said he wouldn't be surprised if hundreds of children had been recruited.
‘This is about the brainwashing and sexual grooming of our young children,' he said.
And last month, it was revealed ISIS had released a guidebook to help young mothers raise a 'Mujahid child'.
'Don't wait until they are seven to start, for it may be too late by then,' it says.
Human Rights Watch has called on ISIS to stop deliberately recruiting children, in particular through weapons training and other military training in school environments.