Militants of the Islamic State group, also known as ISIS, recruited Iraqi orphans into its child soldier division, educating them in jihadist ideology and military techniques, Reuters reported Friday. Many of the children reportedly came from Shi'ite Muslim and Yazidi families, religious communities routinely persecuted by the hardline Sunni Muslim militants who compelled the young boys and girls to refer their families as "apostates" subject to imprisonment and execution. 

Future fighters and militant supporters of the organization's youth army, referred to as "Cubs of the Caliphate," were indoctrinated by radical propaganda that blended elementary school lessons with historical and military terms at a facility in the Zuhur neighborhood of eastern Mosul. ISIS, known for its savvy use of social media and filmmaking, reportedly even developed a mobile app called "Learning the Letters" geared toward educating children in its militant vocabulary, according to Foreign Policy. Materials included letters and pictures for associating words such as "B is for bundaqiyya (gun)," "S is for saif (sword)" and "D is for dababa (tank)." Materials discovered also included a physical education curriculum focusing on martial arts.

ISIS took the Zuhur complex in 2014 and fled in October when the Iraqi military began a U.S.-backed operation to recapture the city from jihadist forces, however, teaching materials and various symbols of the group's presence remained as of last month at least. One former worker, who said he was forced to man the facility by the militants, told Reuters he tried to convince the children to desert when sent off to deadly combat operations against pro-government forces.

"I told them, 'If you see the army, drop your weapons and tell them you are orphans. Maybe they will spare your lives,'" he said.

After taking large swathes of territory in Iraq and Syria in 2013 and 2014, ISIS suffered a series of major losses in recent years. In Iraq, the group faces a coalition of forces led by the Iraqi army and supported by the U.S. along with Kurdish and Iran-backed Shiite militias trying to wrest the militant's grasp on their last major city in the country. In Syria, the militants face off against a number of factions including the Russian-backed Syrian army and its Iran-backed militia allies, rival jihadists, Kurdish forces and various opposition groups backed by the West, the Gulf and Turkey.