Don't say, "Because I'm your mother and I said so."
Truth: Actually, that phrase is a good way to end an inappropriate negotiation. You know the script: You have reasonably explained to your daughter that she must honor her bedtime because children need rest to grow, and she has unreasonably responded, more than once or twice, "But why?" At this point, she is trying to pick or prolong a skirmish, and you are no longer obliged to provide a rational response to her questions, says Anthony E. Wolf, Ph.D., author of The Secret of Parenting: How to Be in Charge of Today's Kids (Farrar Straus & Giroux). Your mission now is to end the discussion -- and "Because I'm your mother and I said so" is a perfectly acceptable way to do that. But if saying it makes you feel too much like your own mom, try substituting this slightly updated version: "Because I'm the mother and you're the child, and there really isn't anything else to discuss."