Mary Poppins by P.L. Travers.

From the moment Mary Poppins arrives at Number Seventeen Cherry-Tree Lane, everyday life at the Banks house is forever changed.
It all starts when Mary Poppins is blown by the east wind onto the doorstep of the Banks house. She becomes a most unusual nanny to Jane, Michael, and the twins. Who else but Mary Poppins can slide up banisters, pull an entire armchair out of an empty carpetbag, and make a dose of medicine taste like delicious lime-juice cordial? A day with Mary Poppins is a day of magic and make-believe come to life!