I am always amazed at the ability that children possess to catch their parents in the act of lying. When you think you have averted a crisis (OK, a mother of a tantrum when you don't have the energy for it) by making a promise you don't intend to keep, it is the one time they remember what you said you would do. And it is the one time that they will keep reminding you of it over and over and over...
So I've learned to bite my tongue when one of the girls wake up in the middle of the night asking for something that has never existed or no longer exists. Like the other night, my almost-three-year-old daughter woke up asking for her pink hairband that has a bow with polka dots.