"Feeding the birds" at Saint Paul's Cathedral, seen as a charitable act of kindness in the film, became forbidden by law in the 21st century, having resulted in excessive defecation from the expanding avian population.
Dick Van Dyke had his heart set on playing Mr. Dawes, Sr., and said they didn't have to pay him, he just really wanted to do it for the fun. Although Walt Disney had offered him the part of Bert right out, he made him audition for the part of Mr. Dawes, Sr.
David Tomlinson (Mr. Banks) also voices several of the animated characters that Bert and Mary Poppins encounter in the chalk drawing, including a penguin waiter and the jockey who allows Mary Poppins to pass on her carousel horse. He also voices the Parrot Umbrella Handle at the end of the movie. Original choices for George Banks included Richard Harris, Terry-Thomas, George Sanders, James Mason and Donald Sutherland.
David Tomlinson was nervous about not being good enough for the part of Mr Banks as he had never sung professionally before.
Matthew Garber was paid 10 cents for every time they filmed the tea party scene. He was afraid of heights, so somebody offered to pay him a "bonus" 10 cents for every take.
Ed Wynn's character, Uncle Albert, was originally written as having a Viennese accent. Wynn, however, didn't attempt the accent - or even an English accent, for that matter. He was just himself, ad-libbing many of the lines he says while laughing on the ceiling in the "I Love to Laugh" scene.
Robert Wise and Ernest Lehman visited the set to view rushes of Julie Andrews' performance. She was cast immediately in the lead for The Sound of Music on the strength of that visit.
Marni Nixon: voice of the singing geese during the "barnyard singalong" segment of "Jolly Holiday".
Walt Disney cast Julie Andrews for the lead after seeing her in "Camelot" on Broadway. When she mentioned she was pregnant, he offered to wait until she had her baby to start filming and offered her then-husband, Tony Walton, the job of designing costumes and some sets for the film. Disney also gave the couple a personally escorted tour of Disneyland and the studio to help them make up their minds.
Walt Disney first attempted to purchase the film rights from P.L. Travers as early as 1938. Travers rejected his advances as she didn't believe a film version would do justice to her creation. Another reason for her initial rejection would have been that at that time the Disney studios had not yet produced a live action film.
Walt Disney was so determined to cast Julie Andrews that he offered to delay filming until the summer of 1964 if Andrews was cast as Eliza Dolittle in My Fair Lady. Since Audrey Hepburn was cast as Eliza, both movies began filming around August/September 1963. (When President John F. Kennedy was assassinated in November 1963, Hepburn, over at the Warner Bros. studios, was hit particularly hardest by the news. She was inconsolable for a few days.)
Julie Andrews initially hesitated in taking on the part of Mary Poppins as she was hoping that Jack L. Warner would ask her to star as Eliza Doolittle in My Fair Lady. That call never came, prompting Andrews to cheekily thank Warner in her Golden Globe acceptance speech.
Julie Andrews provided the whistling for the animatronic Robin during the song "A Spoonful of Sugar".
Julie Andrews was determined to nail the lullaby "Stay Awake". She took nearly 50 takes (most reports suggest 47) in the Disney recording studio to create the perfect "soft" voice quality for the song. Dick Van Dyke, on the other hand, took only one take to record his verses as Mr. Dawes, Sr. on "Fidelity, Fiduciary Bank".
Julie Andrews was left hanging in mid-air during one particularly long camera setup. The stagehands unwittingly lowered her wire harness rather rapidly. "Is she down yet?" called a grip. "You bloody well better believe she is!" fumed Andrews.
Julie Andrews wore a wig in the movie.
Stanley Holloway was originally cast as Admiral Boom, but because he was working on My Fair Lady, he turned it down.
Larri Thomas: the woman in the carriage who blows a kiss at Bert during "Chim Chim Cheree" was Julie Andrews stand-in.
P.L. Travers finally relented and sold the film rights to Walt Disney in 1961, although she retained script approval rights. One of the reasons prompting her to do so was a decline in her book sales.