Who's watching the kids?
Dread is the word. Lang juxtaposes domestic tranquility against danger in such a way that the viewer can sense that something is definitely off-kilter. The children in the ring play happily, but sing a dreadful song. Little Elsie's mother smiles because it's time for her to come home from school, but Elsie nearly gets squashed by a car. The opening elevated shot demonstrates that Mother can see the children, but so can anyone else. The cintog highlights how vulnerable they are out in the open. The most concise image is that of the ball bouncing up against the warning sign on the post--in our minds a child's toy should never occupy the same space as murder, but here it does. The shadow falling across the sign plays with our notions of what we have seen on the screen, because we see M, but not his face. Our minds don't rest well with that ambiguity.
The sound design keeps us off-kilter, too, with the long silences and proto-jump scares of the car horn and the cuckoo clock. The writing underlines the seriousness of the problem. Mother is clearly quite rattled, otherwise why make such a big deal of a ring-a-round-the-rosy type game? She's frightened, and she takes it out on the kids.
These notions of the off-kilter feeling and domestic tranquility merely as a sheer overlay diffusing the evil underneath are threads that run through noir as a style. Noir is LA Confidential digging below the glitz of Hollywood for find that "Everything is suspect...everyone is for sale...and nothing is what it seems." (official tagline) It's that final phrase that captures so much of the essence of noir.