The Hollow Locust Tree — Ann Towell

...three siblings, Hannah, Gabriel and Rafael, growing up in rural Ontario follow the lead of their dog, Lady, and stumble upon a forgotten cemetery. They discover that a black slave family had escaped to the same area in the 1840s. According to the locals, some members of that family are buried on the southeast corner of their farm. Then one night Hannah is awakened by a shout. When she looks out, she sees the slave family climbing the river bank onto the flats of their farm. She wakes her older brother, Gabriel. The two of them boldly venture outside to confront the ghostly figures. But the family disappears, leaving only a slip of paper. The adventure begins...

Young adult novel, based on local legends current in the author's area of Euphemia Township, Ontario, has three late-20th-century children encountering the ghost of an escaped slave child whose family lived on their farm in the 1840s. Unique, interesting time-slip book.