Five years of war have brought a new curriculum to eastern Aleppo’s schoolchildren.

“My 8-year-old son knows all the weapons. He hears the sounds and says, ‘Dad, that was a barrel bomb. Dad, that was shelling,’” said Ali al-Halabi, a father of three.

Out in the streets, children scavenge for bomb fragments, bullet casings and tiny ball bearings, as if they were treasures. “This is their childhood now,” Halabi said.

According to aid agencies, 100,000 children lived in the neighborhoods of rebel-held eastern Aleppo when the area fell under government siege in June. Now, the neighborhoods are being bombarded, and, according to doctors, these young ones are the biggest casualties. At least 300 children have been killed or injured in the past 10 days, a rate attributed to their small frames and softer skulls.

But deep underground, against the odds, one semblance of normality continues. The new semester began this week in several basement classrooms across the city and, come midafternoon, the babble of returning schoolchildren made some in east Aleppo feel that their neighborhoods were still alive.

“They were sounds I used to hate before. Now I just love it,” said Wissam Zarqa, an English teacher from east Aleppo, a city that was once home to 3 million people. “The noise children make in their break has become a sign of life.”

An estimated 97 percent of primary-age children were in school before Syria’s crisis began in 2011. In eastern Aleppo today, enrollment stands at just 6 percent, according to Save the Children.

Through displacement and poverty, many have dropped out or can attend only sporadically. Parents have also been afraid to send their children for fear that they will be targeted.

According to Save the Children, seven teachers and five students have been killed in their underground schools since June. That number is likely to rise now that Russian and Syrian forces are dropping “bunker busters,” powerful munitions that burrow 12 to 15 feet underground before exploding.

“What use is English and math if my boys are killed as they learn? We wish we could send them, but we can’t. It’s too dangerous,” said Hassan, a parent who spoke on the condition that only his first name be used, out of fear for the safety of relatives who have fled to government-held areas.

The underground classrooms are small and lack basic necessities, including fuel to heat or light the rooms. Some are crammed with as many desks as possible. In others, children sit on the floor to increase capacity.

Some parents still believe the classes bring benefits that outweigh the risks and limitations. “Education and knowledge is the only passport for these children's futures, and even in these difficult circumstances, some of the students are quite brilliant,” Halabi said. “When a child is achieving, you forget the dangers outside.” But, as in many families, his decision has led to arguments with his wife, who spends hours each day just waiting for her sons' safe return.

Aid agencies say children who are not in school are more vulnerable to child labor, early marriage or recruitment by armed groups. Underscoring that risk, a video shared online this weekend showed child soldiers tumbling around a training ground run by Jaysh al-Sunna, an Islamic militant group, apparently in northern Aleppo province.

Fear and violence condition the behavior of most children in the area. At home, they play war games and hoard piles of shrapnel. At school, teachers say, they are often withdrawn or violent.

The United Nations Committee on the Rights of the Child warned Monday that it will take decades for the area's children to heal from the mental trauma of war. “We are probably not talking of a lost generation, but quite possibly of lost generations,” said Benyam Dawit Mezmur, the organization's chair.

“Being a parent here is a constant struggle,” said Hassan, reflecting on his decision to pull a son out of school. "Sometimes he is hyperactive and angry, sometimes he is quiet and hungry, small like a little bird. It breaks our heart, but what can we do? There no options left but love."

Above: The U.N. on Wednesday released satellite images showing the most recent destruction in east Aleppo, pounded by Syrian and Russian airstrikes since the collapse of a U.S.-Russia brokered cease-fire two weeks ago.

The U.N. suggested Wednesday that half of east Aleppo's estimated 275,000 residents now want to escape the government's grinding siege, foreshadowing the possibility that humanitarian corridors will be opened to empty the area of civilians.

Before the latest round of bombardment, teachers had tried to run art programs to give children an outlet for their creativity. Most of the drawings featured stick figures running or hiding from warplanes or fire. But one 10-year-old drew himself clutching a clipboard as he surveyed the flattened suburbs of east Aleppo. “This is me and I am an architect rebuilding my city," he wrote. “All my friends will help me."

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