My Pal Gus (1952)
My Pal Gus is a 1952 comedy-drama film which follows Gus (George Winslow) who is the young son of divorced industrialist Dave Jennings (Richard Widmark). Unable to cope with Gus' mischievous streak, Jennings places the boy in a day-care center. Gus' teacher Lydia Marble (Joanne Dru) manages to curb the boy's prankishness, and along the way falls in love with Jennings. Enter the villainess of the piece: Jennings' ex-wife Joyce (Audrey Totter), who claims that the divorce is invalid and demands a huge sum from Jennings, lest she claim custody of Gus.
More at Wikipedia.