Just googled this, found a usually reliable source, the BBC!
https://www.bbc.com/news/amp/world-europe-44518180
Yes, it did happen in Spain, but the max number was 30,000, NOT multiplied by 10!
Further, it was Franco, the fascist dictator who initiated this, taking babies away from Republicans (supporters of the King, and the old regime!) and gave them to fascist families. Some RCC priests may have been involved, but it was not instigated by the church. It was about politics, not religion.
"A slowly unfolding Spanish scandal
In 2008 investigating judge Baltasar Garzón estimated that 30,000 children had been stolen from families considered politically suspect by the Franco regime after the 1936-39 civil war
Some 3,000 reported cases of alleged stolen children have been reported, but prosecutors have closed all but a handful of investigations
In 2013 María Gómez Valbuena, an 87-year-old nun facing two charges of kidnapping and falsifying documents, died before going on trial
In 2017 the European Parliament's Committee on Petitions called on Spain to be more proactive in attending to victims by creating a special prosecutor and a public DNA bank, and urged the Catholic Church to open its archives to shed light on Franco-era adoptions."
There are some estimates of 300,000, but those are estimates based not on records, but speculations. This started in the 1930's, when Franco defeated and disposed the King in a terrible civil war. Ironically, the Spanish brought back the King, after Franco died.
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