Perhaps it was meant to be ironic, calling the 1961 film adaptation of Henry James's 1898 novella, The Turn of the Screw The Innocents. Miles, played by Martin Stephen, and Flora, by Pamela Franklin, are truly evil children. They might as well have been Satan's dynamic duo.
Let us look at the character of Miles in the film. Is he a human or a demon? The character strayed from James's portrayal and went deeper into Sinisterville. I was mortified when Miles showed that wicked little smile to us when he brought flowers to Miss Giddens (Deborah Kerr). When Miles comes home from the trouble at school and is asked by her once again near the end of the movie why he has been sent home, he has mouthfuls of vulgarities and some names he would like to replace hers with. The most evil thing I noticed in Miles is that song. He is singing to "his Lord." I do not think it was the "Lord" that ruled the pearly gates, if you know what I mean.
Now to Flora, the sidekick--she has lovely dresses and dolls to keep her busy. Unlike her counterpart in James's work, she, instead, plays with all of nature's reptiles, a hobby that makes most young girls run in fear; believe me--I know. She has a voyeuristic tendency with her governess, always nosing around and listening in on the conversation. Flora shows her dark heart to us more completely when she encounters the spirit (Clytie Jessop). She follows every command without question or doubt. I think she actually enjoyed and wanted to do everything the ghost told her to.
Some could argue that Miss Giddens is the truly innocent one and the only character not touched by evil. That changes by the end of the film when we see her kiss Miles' corpse with the kind of passion that he had kissed her with earlier. There are no innocents here.