Teenagers carrying weapons stand at checkpoints in Iraq's second-largest city, Mosul. Patched onto the left arms of their black uniforms are the logos of the Islamic Police.
In Raqqa, the Islamic State's de facto capital in Syria, boys attend training camp before heading off to fight. Others serve as cooks or guards at the extremists' headquarters.
Across the region, the group is actively conscripting children for battle, according to a growing body of evidence from residents, activists, experts and human rights groups.
In the Syrian town of Kobani, several activists said they observed children fighting. Mustafa Bali, a Kobani-based activist, said he saw the bodies of four boys, two of them younger than 14. And at least one 18-year-old is said to have carried out a suicide attack.
In Syria's Aleppo province, an activist with the rebel Free Syrian Army said its fighters encountered children in their late teens "fairly often" in battles.
It is difficult to determine just how widespread the exploitation of children is in the closed world of Islamic State-controlled territory. There are no reliable figures.
But a United Nations panel investigating war crimes in Syria concluded that in its enlistment of children, the Islamic State is perpetrating abuses and war crimes on a massive scale.
The panel of experts, known as the Independent International Commission of Inquiry on Syria, conducted more than 300 interviews with people who fled or are living in Islamic State-controlled areas, and examined video and photographic evidence.
The use of children by armed groups in conflict is nothing new.
"What is new is that (the Islamic State) seems to be quite transparent and vocal about their intention and their practice of recruiting children," said Laurent Chapuis, UNICEF regional child protection adviser for the Middle East and North Africa.
In areas of Syria and Iraq, the extremists closed schools or changed the curriculum to fit with their ideology. Their goal, according to the U.N., is to use education as a tool of indoctrination to foster a new generation of supporters.
In Raqqa province, an anti-Islamic State activist collective has documented the presence of at least five known youth training camps.
A video also emerged this month showing two boys, both speaking French, holding guns aloft. French prosecutors have opened a formal investigation to identify the children.
"Over there, you're in a country of infidels. Here, we're mujahedeen. We're in Syria, we're in Raqqa here," one of the boys says. "It's war here."