Note: This is the second episode of a two-part story. However, as Season 5 is the only one with onscreen episode titles, that title is used here, eschewing the practice of numbered parts adopted for previous seasons.
- Kruger - Dana Elcar
- Susie Hayakawa - Judy Dan
- Finster - Ralph Manza
- Simon the Likeable - Jack Gilford
- 99's Mother - Jane Dulo
- Miss Hoskins - Ella Edwards
- Motorcycle Cop - Sid Grossfield
- Intern - Richard Deacon (uncredited)
- Woman in Wheelchair - Rose Michtom (uncredited)
- Narrator - William Woodson (uncredited)
- 99 gives birth to twins in this episode, the only one in which both babies are actually seen. Like her mother and grandmother, the girl is never named but twenty-five years later the 1995 revival series reveals that the boy's name is Zach.
- The title refers to the song "My Blue Heaven" dating from 1924 which includes the lyric "Just Molly and Me/And baby makes Three". A film titled And Baby Makes Three was released in 1949. It is perhaps an unfortunate choice in that it gives away the "surprise" - the fact that the Smart baby is in fact twins.