Dick Van Dyke was offered four options for his dance scene, each with a varying degree of difficulty. He insisted on performing the hardest dance routine and refused any help from fellow cast members while filming the scene. The resulting dance scene was so well received that there were reports of audiences applauding during screenings to see the old actor dance so well for his age.
When Mary Poppins (1964) was being written, the lead role was offered to Dame Julie Andrews by Walt Disney. Andrews told Disney that she was pregnant and couldn't do the movie. Disney wanted Andrews so much that he postponed the production in order to accommodate Andrews' pregnancy. When this movie was announced, history repeated itself as Emily Blunt was also pregnant and the movie was postponed to accommodate her pregnancy.
Dame Julie Andrews turned down a proposed cameo appearance as the balloon lady, fearing that it would be too distracting from Emily Blunt's performance. Julie said, "This is Emily's show, and I really want it to be Emily's show." Quite poetically, the balloon lady part went to Dame Angela Lansbury, who had been considered for the title role of Mary Poppins (1964) in the first movie before Dame Julie Andrews was cast.
Since Dick Van Dyke looks younger than his 91 years, Disney used old age make-up and hair to make him look slightly older.
When Karen Dotrice, who played Jane Banks in Mary Poppins (1964), makes her cameo, before leaving she says, "Many thanks, sincerely." In the first movie, this was the phrase Jane and Michael Banks used at the end of their letter requesting a new nanny.
Karen Dotrice: The actress who portrayed Jane Banks in Mary Poppins (1964), appeared as the Elegant Woman, who asks the Banks family for directions to 19 Cherry Tree Lane. She even repeats a line she sang as Jane in the first movie.