Film
At age eight, Dotrice was hired in 1963 to appear in The Three Lives of Thomasina as a girl whose relationship with her father is mended by the magical reappearance of her cat. Matthew Garber also appeared in the movie. While Dotrice was in California, her father stayed in England—where he was portraying King Lear—and Walt Disney personally took care of her family, often hosting them in his Palm Springs home. Dotrice took quickly to Disney as a father figure, calling him "Uncle Walt". She said that the admiration was mutual: "I think he really liked English kids. He was tickled pink by the accent and the etiquette. And when I was being very English and polite, he would look proudly at this little child who had such good manners."
Film historian Leonard Maltin said Dotrice "won over everyone" with her performance in The Three Lives of Thomasina, and Dotrice was signed to play Jane Banks (along with Matthew Garber as her brother, Michael Banks) in Mary Poppins (1964). Disney's part-live-action, part-animation musical adaptation of the Poppins children's books by P. L. Travers starred David Tomlinson as a workaholic father and Glynis Johns as a suffragette mother who are too busy to spend much time with their children. Instead, they hire a nanny (Julie Andrews) who takes Jane and Michael on magical adventures designed to teach them—and their parents—about the importance of family. Poppins was Disney's biggest commercial success at the time and won five Academy Awards, making its stars world-famous. Dotrice and Garber were praised for their natural screen presence; critic Bosley Crowther wrote, "the kids ... are just as they should be," while author Brian Sibley said, "these charming, delightful young people provided a wonderful centre for the film."
Dotrice and Garber paired up a third and final time in The Gnome-Mobile (1967) as the grandchildren of a rich lumber mogul who stumble across a gnome forest and help to stop the gnomes from dying off. Starring Walter Brennan in a dual role, The Gnome-Mobile failed to perform on a par with Poppins at the box office, and Dotrice did not make another film appearance as a child.
After The Gnome-Mobile, Dotrice and Garber no longer kept in contact with each other. In an interview for the '40th Anniversary Edition' DVD release of Mary Poppins, Dotrice recalled how she learned of Garber's 1977 death:"I remember his mum, Margot, calling [...] to let us know that Matthew had died. That was so unexpected. [...] I wished I had picked up the phone over the years, I wished I had treated him more like a brother; but he's indelibly printed in all of our minds, he's eternal. An amazing little soul."
In another interview she recalled:"[Matthew] was how he looked—an imp, and I loved being his shadow. I can't imagine making movies would have been half as much fun without him. He loved being naughty, finding and jumping off of small buildings on the back lot. While I was Victorian proper and wouldn't let myself get dirty or muddy, Matthew had a great sense of fun and danger. He was a daredevil and could have been a race car driver. And he did live a full life over his 21 years."
In 1977, she appeared with Ann-Margret in Joseph Andrews, a British film based on the Henry Fielding novel Joseph Andrews.
Dotrice appeared as Alex Mackenzie in The Thirty Nine Steps (1978) with Robert Powell and John Mills. The third film based on the John Buchan novel, this was her only feature film as an adult. In the film, Alex accompanies Hannay (Powell) while on the run from "both the spies and the police".
