While its not unusual for authors who have hit it big to "trade up" their agents, editors or publishing houses, the way Ms. Kraus and Ms. McLaughlin have replaced agents bears some resemblance to the way that their books antagonist, the spoiled and unhappy Mrs. X, tears through child-care help. Several sources speculated that though The Nanny Diaries is acid-tongued about chilly Upper East Side wealth, Ms. Kraus and Ms. McLaughlin could reasonably expect to become a part of the very world theyve skewered. Both are from comfortable backgrounds: Ms. McLaughlin grew up in Rochester, N. Y., the daughter of a college professor and landscape designer while Ms. Kraus, whose parents own a bookstore on the Upper East Side, grew up in Manhattan and went to Chapin. The authors have contractual deals for hair and makeup at every public appearance, and they have developed a fondness for writing little notes la Mrs. Xon their own Nanny Diaries stationery.