Jack Clayton didn't want the children to be exposed to the darker themes of the story, so they never saw the screenplay in its entirety. The children were given their pages the day before they were to be filmed.
At one point when Deborah Kerr's character wanders around the house at night with only a candelabra for illumination, you might think you see something in the corner of your eye. You do. It's the clapperboard which had briefly wandered into shot. Jack Clayton decided to keep it in because he liked the idea of something almost subliminal being present to add to the air of unease.
The film opens with a creepy song written by Paul Dehn and Georges Auric sung over a black screen for about 45 seconds before the 20th Century Fox logo appears. In some cinemas, the projectionists assumed this was a mistake on the print and edited the film so it began with the appearance of the Fox logo.
Jack Clayton was dismayed to learn that 20th Century Fox insisted on making the film in CinemaScope. His cinematographer Freddie Francis set about making that less of a problem by framing the wide horizontal frame with lots of vertical lines to break it up. Conversely, he also used the wide space to emphasize shadowy spaces and using the emptiness towards an unsettling effect. To that end, he would often place characters at opposite ends of the frame.
Two of Michael Redgrave's children eventually appeared in different adaptations of the same story. Lynn Redgrave appeared in the 1974 version of The Turn of the Screw, and Corin Redgrave appeared in the 2009 version.
"The Innocents" was the big career break for veteran film editor Jim Clark. They became close friends and regular drinking buddies during the production because they were both recently divorced and lived near each other. In his 2010 memoir "Dream Repairman", Clark described the editing of the film as an easy and pleasurable experience, largely because of Clayton's meticulous approach to film making. Clark also explained how he created unusually long cross-fades for the scene transitions - these ran four or five times longer that standard "4 foot" dissolves and often included a near-subliminal third element in the cross-fades. Clark described Clayton as "a big drinker who used to tipple all day - mostly brandy - and he was a chain smoker". He also noted Clayton's "perverse sense of humor", and expressed the view that Clayton (who, in his view, was "highly influenced" by his earlier contact with John Huston) also emulated Huston's "sadistic sense of practical joking". Clayton's personal assistant Jeannie Sims (who had previously worked for Huston) had been badly burned as a child, leaving her with scars on her hands and face, and she was terrified of fire, but according to Clark, Clayton "made it his business to try and set Jeanie alight as often as possible. He would go to enormous lengths, preparing bonfires that Jeanie would supposedly be put onto." Clark also revealed that, while generally charming, and revered by his crew, Clayton was sometimes prone to outbursts of extreme anger. He recounted an incident in which Jeanie Sims was unavoidably late calling Clayton with the reviews from the London critics' screening of "The Innocents", which Clayton was too nervous to attend. The screening was held up for over half an hour because of problems getting a senior film critic (who was wheelchair-bound) into the cinema, and after Sims finally contacted Clayton by phone, she returned to Clark ashen-faced and explained that Clayton had flown into a rage, and had viciously berated her over the phone for being late. When Sims called Clark to come to Clayton's studio office the next morning, he arrived to find that, the night before, Clayton had completely smashed the large plaster scale model of Bly House (the fictional location for the movie), and that he was refusing to speak to either of them. Although they patched up the friendship, Clark later opined that he felt his close relationship with Clayton had "crossed the line" of the professional relationship between an editor and a director. Although Clark worked with Clayton on his next film, "The Pumpkin Eater" (1964), their professional relationship and friendship effectively ended with that film - after it was released, Clayton inexplicably sent Clark a highly abusive letter, blaming him for the commercial failure of the film - although Clark later postulated that it might have been actually written by Jeanie Sims, because the letter was typed, and he knew that Clayton never used a typewriter.