The Lebensborn program was initiated by the Nazi party to bolster the upcoming generation. They sought to raise children devoted from birth to Nazi ideology; adults might revert back to beliefs and ideals held prior to the formation of the Nazi party, but children could be fully indoctrinated. Meanwhile, any child born with Aryan features (blond hair, blue eyes) was thought to have at least some Aryan blood, even if it had been diluted through interbreeding. The Nazis believed that any such child, no matter what its parentage, could be taught to become Aryan if raised in an appropriately Aryan home.
These two ideas were merged in the Lebensborn program: the process of removing children with Aryan characteristics from their own parents and placing them in Nazi homes to be raised as Nazi children.
Notwithstanding the pain for families who lost children to this program, it at least offered a good chance of survival for their child. But the parents would never hear anything more, and the child would never know its true origins.