``One of these days, this family will find out who I really am. And they are going to be very surprised,'' promises the narrator of this witty, refreshingly contemporary tale. Although she's a member of an ordinary family, she pretends to be a misplaced royal who should be enjoying a life of glamour instead of sharing a room with her baby sister. There's ample room for snobbery, but the authors consistently keep the tone light. Meisel ( Monkey-Monkey's Trick ; Your Insides ) matches debut author Shields's entertaining text with diverting, mock-romantic spreads, surrounding the narrator's pampered alter ego with court attendants (the chef doesn't dare serve lima beans to Her Highness); enviable pets (including a pony, kitten, parrot and snake); and friends who stage riotous slumber parties. In this inviting bit of escapism, Shields and Meisel demonstrate that with a little imagination one's home can indeed be one's castle. Ages 4-8. (Sept.)