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.
As stated in another entry, Ronald Colman was originally supposed to star in this film, when planned in 1957. Coleman passed away in 1958, and in an odd twist, was replaced by George Sanders, who had married Colman's widow Benita Hume in 1959.
The source novel's entitled The Midwich Cuckoos. This is because when cuckoo birds lay eggs, they deposit their eggs in the nests of other (unsuspecting) birds, who then raise the cuckoo chicks as their own. Compounding the insidious nature of this process, the cuckoo chicks often murder their nestmates in competition for food and parental attention.
When little David opens the Chinese box for the chocolate, his father allows a blonde girl to also open the box. In the meantime, her mother is standing off to the side with another blonde boy in her arms. It's obvious looking at all three children that they're played by the same actor. The little girl is wearing a very obvious wig, and their faces are identical.
Except for one sequence, every time the glowing eyes are show, it's a still photograph. At one point, David - after the motorist almost hit one of them - is staring at the man, while a girl next to him is moving. There's a very visible jagged line separating the moving shot from the still frame.