Originally begun in 1957 as an American picture to star Ronald Colman, M-G-M had this scheduled for Spring 1958 and Spring 1959 and postponed both times. Coleman was gravely ill and housebound, dying soon after the script was completed, in an odd twist, his replacement was George Sanders, who had recently married Benita Hume, Colman's widow.
The novel this film was based on was called "The Midwich Cuckoos". The title refers to the fact that when cuckoo birds lay eggs, they deposit them 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 kill their nestmates in competition for food and parental attention.
Except for one sequence, every time the glowing eyes are show, it's a still photograph. At one point, David -- after the motorist almost hits 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.
The baby children were all played by Kim Clarke Champniss, who as an adult would become a very popular Canadian music journalist and television personality, especially familiar as one the original MuchMusic veejays.
The original British release of the film, several months prior to the US release in December of the same year, showed the children's powerful gaze as a deep black-eyed penetrating visage. The US version was altered to give them the frightening, powerful glowing images seen in this version.
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.
When the priest is asked about the pregnant women, he mentions that one of them is a girl by the name Evelyn Harrington. George Sanders (Gordon) previously starred in the movie All About Eve (1950), and the full name of that movie's title character was Eve Harrington.