The Old Willis Place. a ghost story by Mary Downing Hahn.

Diana and her little brother, Georgie, have been living in the woods behind the old Willis place, a decaying mansion, for what seems like forever. A strict set of rules won't allow them to leave the property or even show themselves to anyone. But when a new caretaker and his young daughter, Lissa, come to live there, Diana is tempted to break the mysterious rules for the first time in hopes of making a new friend. She and Georgie learn quickly, though, that breaking the rules can have deadly consequences.