A recent report in the Times on the systematic abduction and Russian indoctrination of tens, if not hundreds, of thousands of Ukrainian children, highlighting two boys who were lucky enough to be rescued, thanks to the Save Ukraine foundation:
"Like thousands of Ukrainian children, the boys were abducted to Russia — part of a programme to re-educate them and turn them into Russians.
Last year the International Criminal Court declared this a war crime, issuing arrest warrants for President Putin and Maria Lvova-Belova, his children’s commissioner, who boasted of taking 720,000 Ukrainian children, including one she adopted herself."
Ukraine is saying "only" 20,000 have been abducted, but even one would be too many. It's suggested that Putin is actively blocking any attempts to rescue further children, and points to another reason for abducting these kids - other than turning them into cannon fodder (as also reported in the link):
"He (Putin) clearly understands every child abducted is a witness to war crimes.”
‘They tried to make us Russians’: the children Putin stole (thetimes.com)