This film was a box-office smash, grossing more money than any prior MGM release in 20 years with the exception of David O. Selznick's Gone with the Wind (1939).
The entire cast and crew were immediately impressed with Vincente Minnelli's attention to detail in every shot. He had consulted author Sally Benson on how the interiors of the Smith home should look, and she had provided a wealth of firsthand information. As a result, the look of each set was near perfection according to the time period. According to Mary Astor, "The only anachronisms were the girls' long-swinging hairdos. Girls 'put their hair up' as soon as they got out of pigtails, the first instant they were allowed to by reluctant parents. It was a symbol, like the first long pants for boys."
The book on which the film is based originally ran as a weekly feature in the New Yorker Magazine in 1942. For the film, many of the actions attributed to Tootie were actually done in real life by Sally Benson's sister Agnes. Also in reality, Benson's father moved the family to NYC, and they never did come back for the World's Fair. Twenty years later, Benson would have sole screenwriting credit on Elvis Presley's biggest box office hit, 1964's Viva Las Vegas.
Following Margaret O'Brien's rapid ascent to stardom, her mother believed they were entitled to a significant raise, and she used this film as leverage, realizing how integral the role of Tootie was to the story. MGM raised the ante by announcing the casting of Sharon McManus in O'Brien's place. McManus was the daughter of a studio electrician and the brass went so far as to fit her with costumes, assuming this would pressure O'Brien's mother into accepting their terms. But she held fast, and MGM was ultimately forced to concede to her demands for the salary increase. Once production was underway, O'Brien was filming a scene when McManus' father, who was employed on the film, intentionally dropped a heavy lighting instrument from the catwalk to the sound stage floor, narrowly missing the pint-sized star. He was taken away and briefly admitted to a mental institution for his deed.