Rosalind Russell was originally considered for the role of the mother (played by 'Nancy Kelly'), until the studio decided to go with the Broadway cast.
Rhoda's murderous grandmother, Bessie Denker, was invented; all the other female career killers referred to in the novel and the film were genuine.
The book Rhoda claims to have won in Sunday School, Elsie Dinsmore , was a story with religious themes about a pious eight-year-old; it was written by Martha Finley in 1867.
The film marked the motion picture debut of Broadway actress Joan Croydon who played Claudia Fern. Although she had also appeared on television, this may have marked her only feature film appearance.
The original Broadway production of "The Bad Seed" by Maxwell Anderson opened on December 8, 1954 and ran for 334 performances.Nancy Kelly won the 1955 Tony Award for Actress in a Drama for "The Bad Seed" and recreated her role in the movie. Patty McCormack, Eileen Heckart, Evelyn Varden, Henry Jones and Joan Croydon also recreated their stage roles in the movie version.
The original ending had Rhoda surviving, and her mother dying. The Motion Picture Production Code in effect at the time, however, required that "Crime shall never be presented in such a way as to throw sympathy with the crime as against law and order." The usual interpretation of this was that criminals weren't allowed to "get away with it." Because of this, the ending was changed: Rhoda's mother survived being shot in the head, and Rhoda herself was killed by a bolt of lighting by a lake.
The piano piece that Rhoda plays and sings and is heard as a theme throughout the film is the traditional French children's song Au Claire de la Lune.
The voice on the radio when Rhoda's mother hears about the drowning at Rhoda's school is that of Henry Jones, who plays LeRoy.
Warner Bros. production notes for the film reported that three endings were shot. According to a Nov 1955 Los Angeles Times , the end of the film was kept secret and the last five pages of the script were not distributed until ready to shoot.