The Nazis thought that some Polish babies and children looked German and kidnapped about 30,000 of them to be adopted by German parents to become Germanized.
Inside Germany, propaganda, the film Heimkehr, depicted these ethnic Germans as persecuted, and the use of military force as necessary to protect them. The exploitation of ethnic Germans as forced labour and persecution of them were major themes of the anti-Polish propaganda campaign of 1939, prior to the invasion. The Bloody Sunday incident during the invasion was widely exploited as depicting the Poles as murderous towards Germans.
After the invasion, Hitler intended to “Germanize” Poland by replacing the Polish population with German colonists. Only enough Poles would be retained as were needed for basic labour, the rest would be driven out or killed. As a first step, Nazi governors in the annexed territories (such as Arthur Greiser in the Warthegau and Albert Forster in Danzig-West Prussia) forcibly deported hundreds of thousands of Poles into the Generalgouvernement.
More than 500,000 ethnic Germans were then settled in these areas. In 1942–43, SS and Police units carried out Germanization actions in the Zamosc region of the Generalgouvernement, forcibly removing some 100,000 Polish civilians, including 30,000 children. In all, at least 20,000 Polish children were taken from their families, transferred to the Reich, and subjected to "Germanization" policies.