"The Sun Comes Up" is mainly based on the 1936 short story "A Mother in Mannville" by Marjorie Kinnan Rawlings. According to the University of South Carolina Libraries description of Rawlings's works, in 1946 MGM asked Rawlings to do a story that could star Lassie with Claude Jarman, Jr. Rawlings started with her 1936 short story "A Mother in Mannville". Although her adaptation never became a novel, the "Saturday Evening Post" published it as "Mountain Prelude", a 6-part serial during April 26 to May 31, 1947.
Helen Winter (Jeanette MacDonald) drives a 1948 Ford Sportsman Convertible.
Jeanette MacDonald had to be under constant medication because of her severe allergy to dogs.
One of the orphans is played by Tommy Rettig who, 5 years later, starred in the Lassie TV show.