Russia used a network of 43 centres to “relocate" more than 6,000 Ukrainian children from their homes after invading its neighbour on February 24, a report by Yale University’s School of Public Health found.
The study, by the school's Humanitarian Research Lab, found Russia was using a network of summer camps spread out across Russian-occupied Crimea and elsewhere to “relocate” and “re-educate” Ukrainian children.
The US Department of State called Russia's children’s camps a “war crime".
Russian President Vladimir Putin "seeks to rob Ukraine of its future by taking its children", said State Department spokesman Ned Price said.
“Russia's system of forced relocation, re-education and adoption of Ukraine's children is a key element of the Kremlin's systematic efforts to deny and suppress Ukraine's identity, its history and its culture."
According to the report, parents are often forced to sign over power of attorney of their children while under “duress”, and their wishes are routinely “ignored”.
The network, which stretches across Russia, appears to be part of a hearts-and-mind campaign by Moscow.
Ukrainian children are exposed to pro-Russian propaganda and “Russia-centric academic, cultural, patriotic, and/or military education", the report says.
Released on Tuesday, the report, which is backed by the US government, gathered evidence through open sources including social media posts and news reports.
Researchers believe the network is co-ordinated by Moscow and involves "every level" of Russian government.