The Bad Seed(1956)
A mother named Christine Penmark lives with her husband (currently away on military duty) and their daughter, Rhoda. Rhoda is a well, proper and sweetheart, Later it turns out a young boy has drowned at Rhona's school, Christine start to unravel that Rhoda may not be the good girl everyone think she is.
Based on the play and novel of the name, by play Maxwell Anderson, and William March.
Directed by Mervyn LeRoy.
This is a video trailer for the movie.