Based on the real-life Gilbreth family. Daughter Mary died from a childhood illness; the movie includes a Mary but keeps her somewhat in the background with no lines.
The big house the family moves to in Montclair is the same house set originally built for Judy Garland's family in Meet Me in St. Louis (1944). Fox didn't have an appropriate standing outdoor set so they rented time on the "St. Louis Street" on MGM lot #2.
Frank Gilbreth: [while escorting Ann out of the house on her first date]
I know its not your fault Lilly, but things would have been a whole lot easier if you'd taken my advice and had all boys.
Man on street:
Hey Noah, what are you doing with that Ark?
Frank Gilbreth: Collecting animals like the good Lord told me brother. All we need now is a jackass. Hop in!