The Twenty-Four Days Before Christmas — Madeleine L'engle

To seven-year-old Vicky Austin, the twenty-four days before Christmas are the most wonderful days of the year. She's going to be an angel in the Christmas Pageant. Best of all, Vicky and her brother John and her little sister Suzy do something special every day to celebrate: they hang twinkling lights, make cookies, and wish very hard for snow.

But what if the new baby comes during Christmas and Mother has to go to the hospital? How can they have Christmas without Mother?