The Islamic State has grown its ranks by an estimated 400 children who were recruited by the terrorist organization in combat, espionage, and propaganda roles as part of its "Cubs of the Caliphate" initiative.

"They're central to the ISIS media strategy of trying to garner outrage and shock the world," said Charlie Winter, researcher at anti-radicalisation thinktank Quilliam. "It's all part of ISIS's attempt to show themselves as a functioning state with a proper education system."

The Syrian Observatory for Human Rights issued a report stating that these children were recruited near mosques, schools, and public play areas because the Islamic State has been having difficulty recruiting adults recently. The Observatory head, Rami Abdulrahman, says that only 120 adults have been recruited to ISIS since the start of the year.

But, as frightening as it may sound, the lower recruitment numbers have less to do with interest and more to do with the crackdown of refugees heading to join ISIS from other countries.

Turkey's parliamentary speaker Cemil Cicek says that over 12,500 people from 93 countries have been captured in the country trying to cross over to Syria to join ISIS. But the children already in Syria are just easier to capture.

"They use children because it is easy to brainwash them. They can build these children into what they want, they stop them from going to school and send them to IS schools instead," Abdulrahman said.

While some of the children are recruited with their parents' consent as part of a "military training exercise," several more have been kidnapped without their parents knowing. The children are taught to handle and fire live ammunition, how to drive, and even how to behead.

In a report made back in September, Syria Deeply says that young children in Syria were given a large knife and a blue-eyed, blonde-haired doll to take home for homework. The assignment? To learn how to behead the dolls.

The group also encourages children with birth defects to join their ranks, as some believe that these children are used as human shields, blood donors for wounded fighters, and suicide bombers.

In a video released earlier this month, a French child is shown executing 19-year-old Arab-Israeli citizen Muhammad Musallam who was accused of being a spy. Unlike previous videos featuring adult executioners, the young boy's face was left uncovered. Experts believe this was to further drive home the fact that the boy, who looked to be around 12 years old, was so young.

Newsweek points out that the same techniques used to recruit and charm these children are often used by pedophiles. "I think to speak of children joining ISIS is not a good way to put it," Charlie Winter continues. "Even if they have the perception of choice, it's not choice. If you're a minor and being indoctrinated from a very young age, you don't have the power to make a serious choice. I think that it's certainly worth considering more robustly that people are being groomed."