At the beginning of the story, an unusual and inexplicable event has knocked out everyone in a two-mile radius in the town of Midwich. Richard Gayford and his wife, after trying to sneak in from out of town, get knocked out as well. The townspeople call this the "Dayout." Soon after, every woman of childbearing age in the town realizes they are pregnant, and they give birth to unusual children—31 boys and 30 girls—all with silvery skin, blonde hair, and golden eyes. None of them seem to be biologically related to their parents, and they grow quickly. It is revealed later that they have telepathic powers and that each gender shares a hive-mind. They begin studying with Gordon Zellaby.

The townspeople learn that this event occurred in several other locations around the world, but the people in these places all took different actions as a result. An Inuit tribe had immediately killed the Children when they were born, knowing they weren't their own children. A Soviet town had been destroyed in its entirety by a nuclear weapon after the Children had grown for some time.

Realizing they must destroy the Children, the townspeople begin to try and attack them, but they are turned against one another by the power of the Children's telepathy. When the Children realize that the people plan to bomb them, they refuse to leave, knowing that an aerial bombing will kill the people in the town as well, and they use their abilities to redirect planes away from Midwich. They plot to fly to a remote location and create a colony, which could have destructive consequences for Earth.

Zellaby, the only individual they trust, realizes they cannot be stopped. Because he is already dying, he smuggles a bomb into his classroom and detonates it when all of the Children are watching a film. He perishes, along with all of the Children, saving the town and the world.