KYIV - As Russian forces laid siege to the Ukrainian city of Mariupol last spring, children fled bombed-out group homes and boarding schools.

Separated from their families, they followed neighbours or strangers heading west, seeking the relative safety of central Ukraine.

Instead, at checkpoints around the city, pro-Russia forces intercepted them, according to interviews with the children, witnesses and family members. Authorities put them on buses headed deeper into Russian-held territory.

“I didn’t want to go,” said Anya, 14, who escaped a home for tuberculosis patients in Mariupol and is now with a foster family near Moscow. “But nobody asked me.”

In the rush to flee, she said, she left behind a sketchbook containing her mother’s phone number. All she could remember were the first three digits.

Since Russia’s invasion of Ukraine began in late February, Russian authorities have announced with patriotic fanfare the transfer of thousands of Ukrainian children to Russia to be adopted and become citizens. On state-run television, officials offer teddy bears to new arrivals, who are portrayed as abandoned children being rescued from war.

In fact, this mass transfer of children is a potential war crime, regardless of whether they were orphans. And although many of the children did come from orphanages and group homes, authorities also took children whose relatives or guardians want them back, according to interviews with children and families on both sides of the border.

As Russian troops pushed into Ukraine, children like Anya who were fleeing newly occupied territories were swept up. Some were taken after their parents had been killed or imprisoned by Russian troops, according to local Ukrainian officials.

This systematic resettlement is part of a broader strategy by Russian President Vladimir Putin to treat Ukraine as a part of Russia and cast his illegal invasion as a noble cause. His government has used children – including the sick, poor and orphaned – as part of a propaganda campaign presenting Russia as a charitable savior.

Through interviews with parents, officials, doctors and children in Ukraine and Russia, The New York Times identified several children who had been taken away. Some returned home. Others, including Anya, remain in Russia.

The Times interviewed Anya several times through instant messages, exchanged voice memos with her and verified key details through her friends, photographs and a journal she kept identifying other children she had been with. She asked reporters not to contact her foster parents, who had told her not to talk to outsiders.

Anya had lived apart from her mother and was in only sporadic contact with her before the war. Without the phone number, Anya said she could not reach her.

At first, reporters could not, either.

The Times is not identifying Anya’s full name. A shy girl with a passion for drawing, she said that her Russian foster family treated her well but that she ached to return to Ukraine. Soon, though, she said she would become a Russian citizen. “I don’t want to,” she said. “My friends and family aren’t here.”

Anya and others described a wrenching process of coercion, deception and force as children were shipped to Russia from Ukraine. Together, their accounts add to a growing body of evidence from governments and news reports about a removal-and-adoption policy that targets the most vulnerable children in the most dangerous situations.

Transferring people out of an occupied territory can be a war crime, and experts say the practice is especially thorny when it involves children, who may not be able to consent. Ukrainian officials accuse Russia of perpetrating a genocide. The forced transfer of children, when intended to destroy a national group, is an act of genocide under international law.

Russian officials have made clear that their goal is to replace any childhood attachment to home with a love for Russia.

While the resettlement of children from newly occupied lands has so far been sporadic, the Russian government recently announced plans to resettle these children more efficiently, raising the prospect of many more transfers.

Russia’s wartime tactic exploits some of the thorniest and most intimate family dynamics. Russian families spoke of adoption as a matter of patriotism, but they also expressed a heartfelt desire to provide a better life for the children. And while many Ukrainian parents try to recover their children, others do not, whether for financial reasons or because their relationships were severed even before the war.

In the Siberian city of Salekhard, along the Arctic Circle, Olga Druzhinina said she adopted four children, ages 6-17, from around the Ukrainian city of Donetsk, more than 1,600 miles away. Russia recently illegally annexed the Donetsk region and three others in eastern and southern Ukraine.

“Our family is like a small Russia,” Druzhinina said in an interview. “Russia took in four territories, and the Druzhinin family took in four children.”

She said she was awaiting a fifth child and considered the children fully Russian. “We are not taking what is not ours,” she said. NYTIMES