This is a very interesting piece in Der Spiegel on the baby snatching phenomenon in Spain:
All of these women share a similar fate. From the beginning of the Spanish Civil War, in 1936, until well into the 1990s, more than 300,000 children were reportedly taken from their biological parents and passed on to adoptive parents.
In regions captured by the anti-communist Nationalists during the war, doctors and nuns felt it was their patriotic duty to take newborns from “red parents” and give them to other families. There, they were to be raised in accordance with Nationalist and Catholic beliefs.
After the victory of the rebels under General Francisco Franco over the Republicans, the organized theft of babies became a political tool, a way of depriving leftists of their offspring. In 1941, Franco enacted a law that made it permissible to erase evidence of the ancestry of such children by changing their last names.
Most of these stolen children were entrusted to the care of Catholics loyal to the regime. The aim behind this was to rid an entire people of the “Marxist gene,” at least according to the theories of Antonio Vallejo-Nájera, the national psychiatrist of Francoist Spain, that were widespread at the time.