bdullah Abu Nada was working in his laboratory at Gaza City’s biggest hospital last month when his friend came in with chilling news: The house where his wife and four children were sheltering had been hit by an Israeli airstrike.
As survivors of the attack began arriving at the emergency room, Abu Nada, a chemist, rushed through the chaotic halls, searching for his family. One small boy had been pulled from the rubble, but when soot was rubbed from the child’s face, it was clear it wasn’t Abu Nada’s youngest son.
It would be days before rescue workers found the broken bodies of Abu Nada’s wife and four children in the debris.
“Sometimes he remembers them and starts saying: ‘Oh yes, Ahmed, yes, I am coming,’” said Abu Nada’s brother, Omar Abu Nada. “He can’t get over the shock.”
The expanding Israeli military campaign to end 16 years of Hamas rule in the Gaza Strip is taking a heavy toll on the enclave’s young.
More than 3,900 Palestinian children have been killed in four weeks, or roughly 40% of people who have died in Gaza as a result of Israeli strikes, according to the Hamas-controlled Gaza health authorities. On Saturday, Gaza health officials said another 1,200 children are missing and their bodies are believed to be buried under rubble. Overall, more than 9,400 Palestinians have been killed, according to the Ministry of Health, which doesn’t distinguish between militants and civilians.
Gaza’s population is among the youngest in the world, with nearly half being under the age of 18, according to the nonprofit Population Reference Bureau in Washington.
Jason Lee, the Save the Children charity’s country director for the West Bank and the Gaza Strip, said “Gaza has become a graveyard for children” with more than 400 being killed or injured each day.
“The numbers are harrowing and with violence not only continuing but expanding in Gaza right now, many more children remain at grave risk,” he said.
On Friday, the World Health Organization and several United Nations agencies said the Israeli invasion is taking a disproportionate toll on women, children and newborn babies in Gaza—who represent 67% of all casualties, according to Gaza medical officials.
“The bombardments, damaged or non-functioning health facilities, massive levels of displacement, collapsing water and electricity supplies as well as restricted access to food and medicines, are severely disrupting maternal, newborn, and child health services,” said the World Health Organization and U.N. agencies, including Unicef.
Israel launched its military campaign on Oct. 7 after hundreds of Hamas militants from the Gaza Strip carried out a series of attacks that killed more than 1,400 people, most of them civilians, according to Israel. More than 240 other people were kidnapped and taken back to Gaza as hostages.
The Israeli military has carried out thousands of airstrikes, bringing down high rises, transforming neighborhood blocks into rubble and prompting more than half of Gaza’s 2.2 million residents to flee their homes. The Israeli military says it is targeting Hamas offices, militants’ homes and weapons storage sites that are intermingled with the civilian population.
The campaign is taking a much higher toll on women and children than previous conflicts in Gaza, according to statistics. Men accounted for about 60% of the deaths in wars in 2008-2009 and 2014, U.N. data shows. This time, they make up about 34% of the deaths, according to Palestinian health authorities.
Zaher Sahloul, a Chicago doctor who has worked in the Gaza Strip as head of MedGlobal, a nonprofit group that sends medical professionals into conflict zones, said children are less able to withstand injuries from airstrikes and Gaza lacks much of the medical support that could save their lives.
“This is the worst that we’ve seen,” he said. “Most of the injuries that adults can survive, children cannot.”
Hussam Abu Safiya, director of the pediatric ward at Kamal Adwan Hospital in the northern Gaza Strip, said that he and his colleagues have struggled to treat injured friends and family members rushed to their hospitals.
“The injuries and the number of deaths are beyond imagination,” he said. “This is the first time in my life that I’ve witnessed such a thing.”
“When you are a physician dealing with mass casualty incidents you are focused on the moment and the patients,” Sahloul said. “Then you discover that this kid is someone you know, your nephew, or niece, or your neighbor’s kids, or even your son. That’s the most horrible thing that will happen to anyone.”
On Oct. 13, Abu Nada was working at Al-Shifa Hospital in Gaza City. The Israeli military had urged residents to flee south in the early days of the war. But he wanted to keep his family close, so he first moved them to his hospital, which the Israeli government says Hamas militants use as a command center, making it a potential target for attack.
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Abu Nada then sent his family to stay with his brother-in-law at his home across town, where he hoped they would be safer. He had been reluctant to send them away. The children liked playing in the hospital.
“I want to come get you,” Abu Nada told his wife, Samah, a 39-year-old teacher at a U.N. school in Gaza, Omar Abu Nada said.
Four hours later, Omar Abu Nada said, the Israeli military warned that it was going to target the neighborhood where the doctor’s family had moved. An Israeli airstrike hit a five-story building where the Abu Nadas and four other families were staying, killing 27 of the 32 people inside, he said.
The Israeli military didn’t comment on the specific airstrike and said that it had repeatedly urged Palestinians to leave Gaza City and move south for greater safety.
When word of the strike reached Abdullah Abu Nada at the hospital, he sent his wife a message. The message went through, but he got no response. Abu Nada called his wife but couldn’t get through. The doctor called his 15-year-old son, Ahmad. No reply. He called his 16-year-old daughter, Nawal. No answer.
Omar Abu Nada jumped in an ambulance and rushed to the home, where he saw rescue workers climbing through the collapsed building in search of survivors.
“I’m alive,” he heard one girl cry from under the rubble. “Come and get me!”
After six hours’ work, the rescue team pulled the girl from the rubble before dawn. But there was no sign of Abdullah Abu Nada’s family before the rescue teams took a break.
It took rescue workers six days to pull the victims out. Along with his wife and two oldest children, Abdullah Abu Nada lost his 12-year-old son, Anas, and 8-year-old Mohammed, his youngest. Their bodies had all been torn apart by the blast, Omar Abu Nada said.
“I identified Ahmad by the way he sleeps,” he said. “He was holding a mobile phone in his hand. Mohammed was identified by his small hand. Nawal, we were only able to dig out half of her body. Her other half is still under the rubble.”
Their bodies were wrapped in white shrouds and buried together in a mass grave.
Suha Ma’ayeh and Dov Lieber contributed to this article.
Write to Dion Nissenbaum at dion.nissenbaum@wsj.com