Mixed Company is an American movie from 1974, directed by Melville Shavelson.
The spanking scene
The first child adopted by the family is 14-year-old Freddy (played by Haywood Nelson), a black boy. There is a scene where Freddy misbehaves in the bathroom, which is flooded with soapsuds. The boy then gets an OTK on-the-spot spanking by his adopted father (M/m).
The film has casual, nonsexual nudity.