Pulling together some of the things I gleaned from the DVD extras:
- The movie was adapted from a series of New Yorker sketches by a writer named Sally Benson (who wrote Shadow of a Doubt for Hitchcock!) about her youth in St. Louis. A lot was invented and added (including the drama of the potential move to New York, I think), but all of the children’s names are taken directly from her story and life; she was “Tootie.”
- Already mentioned in a comment: in the original version, the lyrics to “Have Yourself a Merry Little Christmas” went like this, “…It may be your last…” Like a Christmas horror movie!! Judy Garland told the songwriter that people would think she was a child abuser if she sang that to Tootie, so he revised the lyrics.
- The songwriter also commented that they had directions from Minnelli to write a song for the trolley scene “about a trolley.” They kept hinting to him, “does it have to be a song about a trolley? Can’t it just be sung on a trolley?” But he insisted.
- The movie was a groundbreaking musical in the way all of the music is integrated diegetically, as part of the narrative itself (characters singing at a party or the like); I don’t think there are any songs that interrupt and stand apart from the narrative world of the story.
- Margaret O’Brien explains that Garland seemed to feel a special bond with her as a child actor/star; Garland said something like “she has no life of her own, and I know what that’s like.” (Garland was I think 21 at this point — she married director Vincent Minnelli a year later). But O’Brien commented that this wasn’t really true; by this time, child labor laws had become routinely enforced in Hollywood; she always had a teacher present on set, rules were enforced for the number of hours she could perform a day, and so on. She said this was completely different from Garland’s experience as a child, kept up all night with uppers to perform. Really sad.
- Big debate over what it took to get Tootie to cry hysterically for that killing-the-snow-family scene. Minnelli says that on O’Brien’s mother’s advice, he told her that her dog had been kidnapped and shot. In her interview, O’Brien flatly denies this on the grounds that it would have been too sadistic, but my sense was that she might have misremembered and misunderstood, because Minnelli was clearly suggesting that O’Brien understood it at the time as a fiction and an acting exercise: he said she asked “was there a lot of blood?” (which sounds very Tootie) and then when she was ready, went out there and bawled. She claims however that she had an ongoing competition with another actress (I forget who), and all her mother had to do was say “boy, so-and-so was really crying up a storm” and she’d rise to the occasion. O’Brien also said that the hardest part of the Holloween scene was to act scared, because everything was so much fun, the mean old man was really nice, the supposedly fierce attack dog was a sweetheart, etc. I would like to know more about her life… I hope she was not miserable as a washed-up child star. [I could check this out although it sounds more like a factual resource/compendium than a narrative biography.]