Katie Nanna is a minor antagonist in Mary Poppins.
At the beginning of the film, Katie Nanna is the nanny to Jane and Michael Banks. Just before the film begins, she had apparently taken them on an outing to the park, and they had, in her words, run away from her. They apparently had a history of misbehavior, as they had run away 3 times in just that week, and she had grown fed up with it.
Katie Nanna does not appear after the opening of the film, but she is referenced during the initial search for a new nanny, where some of her background is revealed. When George and Winifred Banks discuss her failure, it is revealed that she was the last of six nannies hired over a course of four months, and that none of them had succeeded. Winifred had hired her, due to her solemn and cross appearance, which led Winifred to believe that she would be firm with the children.
Role in the film
As the film opens, she has packed her things and is preparing to leave, as she has chosen to resign. The Banks' cook, Mrs. Brill, and maid, Ellen, are shown to have differing opinions on the impending resignation. While Mrs. Brill is happy to see her leave, Ellen attempts to convince her to stay, as Ellen is usually tasked with child care in the absence of a nanny.
However, Katie Nanna's departure is delayed by the return of Winifred. While she sings her introductory song, "Sister Suffragette", Katie Nanna attempts to inform her of her coming departure. Winifred finally asks her where the children are. When she informs her that they have gone missing, Winifred scolds her for allowing it to happen as it was the fourth time that week. She then asks Winifred for her wages, as she has chosen to resign rather than deal with the badly behaved children. Winifred tries to convince her to stay, citing that Mr. Banks had just gotten used to her. Nothing can convince her, and so she leaves, running into George as she enters her taxi. She isn't seen again for the rest of the film.