Jill Krementz remembers wondering, when she was taken to the Nutcracker, how all those children got on that stage. Others like her, and all those little girls taking ballet, or wishing they could, will no doubt envy ten-year-old Stephanie, first seen practicing at the barre at the School of American Ballet (whose students ""get to be in a lot of the real ballets because Mr. Balanchine uses lots of children""). Then, in an atmosphere of tension, primping, and hovering mothers, Stephanie is ""picked"" to be Mary in the Nutcracker and Krementz takes us through rehearsals--with reminders by teacher David Richardson to ""keep my stomach in"" and Mr. B. himself showing her how to faint--and then all through the opening performance and the flowers (""They were so pretty"") and fame that follow (""Some. . .asked me for my autograph""). Putting Krementz's words in Stephanie's mouth doesn't really bring her closer as her statements all seem so calculatedly conventional, and Stephanie's bandbox looks and perpetual poise don't help either. (We can't help comparing the scene to the twirling tournaments of less priviledged princesses). Impressively packaged, this has the air of a too well-rehearsed production--but that certainly won't dim the stars in the eyes of Stephanie's audience.