They also perceive their parents to be essentially omniscient, a belief that won't be completely destroyed until the 20-kiloton blast of puberty. The fuse gets lit early, though, around 36 months, when kids begin to realize that parents can't always read their minds. To their delight (or horror), children discover they can give their parents false information without its being detected. Or, at least, they think they can. The child's realization that you can't always read his or her mind coincides with the flowering of something we call Theory of Mind skills.
What is Theory of Mind? This video explains: