This is a story most of us know, whether from the book or from the 1964 Disney movie. Recently it has gotten a flurry of new attention due to the new Disney movie about making the Mary Poppins movie, Saving Mr. Banks.
Mary Poppins arrives, apparently on the East Wind, at 17 Cherry Tree Lane, London, when the Banks family is in dire need of a new nanny, Katie Nanna having quit and departed quite abruptly. She is brusque and high-handed, and promises only that she will stay until the wind changes, but magical things happen all around her.
It's a charming story, and well worth reading whether you are in the intended age group, or long removed from that.