
The Green Knowe series moves across time and focuses on different sets of characters, but one thing is always the same: the old house called Green Knowe. Green Knowe is an English manor house, which has been owned and lived in by the Oldknow family for generations. The house is inhabited by the spirits of the some of the ancestors of the Oldknows and surrounded by magic that allows people to see mythical creatures and travel through time.
The series is by Lucy M. Boston.
Books in the Series:

The Children of Green Knowe (1954)
Toseland, called Tolly, comes to Green Knowe to spend Christmas with his great-grandmother, learning more about the history of his family and interacting with the spirits of some of his ancestors.
The Chimneys of Green Knowe (aka Treasure of Green Knowe) (1958)

The River at Green Knowe (1959)
Two elderly ladies, Doctor Biggin and Miss Bun, have rented Green Knowe for the summer and are staying there with Doctor Biggin’s niece and two refugee children. As the children explore the area around the house, they meet fantastic creatures and witness amazing things.
A Stranger at Green Knowe (1961)
One of the children from the previous book, Ping, is staying with Mrs. Oldknow at Green Knowe.
An Enemy at Green Knowe (1964)
Mrs. Oldknow tells Tolly and Ping about a necromancer who used to live at Green Knowe as a tutor, called Doctor Vogel, and a mysterious professor comes to Green Knowe in search of Doctor Vogel’s papers.
The Stones of Green Knowe (1976)
The son of the man who built Green Knowe, Roger, finds two stones shaped like thrones that allow him to travel through time and even meet some of the modern residents of Green Knowe who have appeared in previous books.