Mary Poppins in the Park, Paperback/P. L. Travers

Who else but Mary Poppins can lead the Banks children on such extraordinary adventures? Together they all meet the Goosegirl and the Swineherd, argue with talking cats on a distant planet, make the acquaintance of the folks who live under dandelions, and celebrate a birthday by dancing with their own shadows. And that's just for starters