Mary Poppins lyricist Robert B. Sherman had searched for nearly two weeks for a catchy phrase that could be Mary Poppins’ anthem. He came across the perfect title when his young son Jeff came home from school one day and announced that he had just received a polio vaccine. Thinking that the vaccine had been administered as a shot, Sherman asked, “Did it hurt?” He replied, “No. They just gave it to me on a cube of sugar and I swallowed it down.” Sherman tried the idea on his brother the following morning, Richard M. Sherman put the phrase to music and “A Spoonful of Sugar” was born.
Julie Andrews provided the whistling for the animatronic robin during the song “A Spoonful of Sugar”. For her interaction with the robin, Andrews had yards of control wires hidden under her costume and running up her sleeve.
Originally in the movie, there was a scene when all of the toys in the nursery come alive. Since it proved to be too scary for children, it was cut out. However, in the Broadway musical of Mary Poppins, the toys coming alive idea is used. –IMDB