Five-year-old Elisa has an older brother and a new baby brother, but her elderly neighbor says the middle is the best, just like the filling in a sandwich.
As the months pass during first-grade teacher Mrs. Neal's pregnancy, her class gets involved writing letters to the baby, thinking up possible names for it, and designing a baby room on the bulletin board.
Katie, an ordinary third-grader who accidentally wished on a shooting star to be anyone but herself, turns into her best friend Suzanne's baby sister, but the real trouble starts when she speaks, causing everyone to think the baby is a genius.
Adam Joshua and his classmates become even more anxious about the approaching maternity leave of their favorite teacher Ms. D. when they are each assigned an egg baby in a class project about parenting.