After explaining the words of Jadis the witch to Digory after the latter had picked the fruit for Aslan (The Magician's Nephew, "An Unexpected Meeting"), my 5-year-old asked me: "can bad guys pretend to be good?", referring to Jadis. My answer was a most emphatic "oh, yes!" I might have pointed out that it is most rampant during election time, but I didn't want to complicate it for him. He'll find out soon enough, when he's old enough to are about voting. Why, it's all the rage in politics.
[Thanks to the American Papist for pointing out a good example.]