According to Pat Cardi, director William Castle wanted something different for the ending but the MCA Universal executives choose the one that the crew called a lousy ending.
William Castle wanted the sum of money the two kids inherited from their father was twenty millions instead of ten millions, as it was in the novel the film was inspired from. But a MCA Universal executive producer replied that for twenty millions he would kill the two kids himself.
Even though Herman Stein is credited with the score, there is no original score by him for the film and it is a track job of cues from other films.
According to Pat Cardi, director William Castle was very attentive with the children, he followed their advises concerning the way the kids talked in real life, for the dialogues.