The Book of Stone (1969) on Netflix

Plot summary

Julia Septién comes to the house of Eugenio Ruvalcaba to serve as governess for his daughter Silvia, and Eugenio introduces her to his wife, Mariana. The girl plays with a companion named Hugo, and Julia takes the boy for a neighbor until Eugenio tells her Hugo is not real and sends her to the lake, where a stone statue of a boy who holds a book stands. He says the statue came with the property and that Silvia has behaved strangely since it arrived. The gardener, Bruno, complains that someone stepped through the flowers under the dining room window. Julia learns that no other houses stand nearby, yet she keeps thinking Hugo may be a real child who comes to play.