Deception is rampant in Childhood's End. Deception is a trick of knowledge; the less you are deceived, and the better you are at deceiving others, the more powerful you are. The best deceivers are, of course, the Overlords, who deceive mankind on dozens of different points. Karellen deceives Stormgren by hiding behind a piece of one-way glass and calling it a "viewscreen" and by planting a tracking device on Stormgren. Stormgren, for his part, sneaks a scanner into Karellen's room and then tries to use a flashlight to see through the glass. Karellen has the greater power, of course, because he is aware of both of Stormgren's deceptions, just as he is (almost certainly) aware of Jan Rodricks's plan to sneak aboard an Overlord vessel many years later.
The Overlords deceive humanity from the start, never revealing their intentions until the children of the last generation begin to mutate into the Overmind. The Overlords visit New Athens under the pretence of inspecting the island, when actually they just want to check up on Jeffrey. Stormgren's kidnappers try their hardest to trick the Overlords. Jan does his best to deceive the Overlords when he sneaks on to their ship. Deception is a major tool of intellectual control, and though the Overlords are the masters of it, it is the primary weapon of both humans and Overlords throughout the novel.
Christian Imagery and Folklore
As frequently discussed elsewhere in the summary analyses, Childhood's End often seems like an allegorical tale, a morality play set on a science fiction stage. The play features the arrival of the Antichrist, or Satan (the Overlords), the end of humanity (as it dies out after the Overlords' announcement of the coming of the Overmind), and an Armageddon and assumption of the "faithful" into "Heaven" (as the children of the last generation join the Overmind, destroying the Earth in the process). Considering its unique and transcendental nature, when compared to the rest of Clarke's works, it seems entirely reasonable to look at Childhood's End as a thinly-veiled fable with some significant social commentary (particularly about the nature of utopias), rather than a work of serious science fiction.
Part of the description of the Overmind is that it is a kind of "collective conscious," a being of thought and energy composed of the minds of millions or billions (even trillions?) of other beings, all working as a single entity. As a race, all humans—even those thousands of years before the children of the last generation—have had some latent abilities of this sort. This is what provides the explanation for why the Overlords look so similar to a Christian image of the Devil: humans, as a collective, had a premonition of their ultimate end, and they feared that end. Therefore, they made the participants of that end, the demons, into an object of fear and evil. This collective consciousness also appears in specific people such as Jean and Jan, who often have slight premonitions before major events occur.