Ronald Colman was originally supposed to star in this film. He passed away in 1958 and was replaced by George Sanders, who had married Colman's widow Benita Hume in 1959
Originally begun in 1957 as an American picture to star Ronald Colman, MGM shelved the project, because it was deemed potentially inflammatory and controversial, specifically due to its sinister depiction of virgin birth.
The blond wigs that the children wear had a built-in dome to give the impression that they had a larger than normal cranium.
The eerie effect of the children's glowing eyes was created by matting a negative (reversed) image of their eyes over the pupils when they used their powers.