I recently watched the terrific British film Tiger Bay (1959). It's the story of a young girl who befriends a Polish sailor on the run from the law. Horst Buchholz plays the sailor, and the young girl is played by 12 year old Hayley Mills, making her acting debut.
The role of the child had been intended for a young boy. But when director J. Lee Thompson was visiting the home of Hayley's father, actor John Mills, who had been cast as the police inspector in the film, the director had a better idea. He was so taken with Hayley that he offered her the part without an audition.
She's remarkable in the film, and won the BAFTA Award for Most Promising Newcomer for her performance. In the the next few years she made several films for Walt Disney, and rocketed to stardom. As a young boy I'd seen Mills in her Disney films, but I did not remember what a huge star she was in the early 1960s. Stanley Kubrick offered her the lead in Lolita, but her father turned it down. "I wish I had done it", she said in 1962. "It was a smashing film."
I highly recommend Tiger Bay. The script is tight, the characters well drawn, the milieu of immigrants in the Tiger Bay district of Cardiff is fascinating, and it has the look and feel of a noir. If Thompson made a better film I haven't seen it.