What was the tragic movie about a mother who dies and sons put in foster care and take place in the 1920s?

The movie you're referring to is likely "The Last Picture Show" or "The Great Santini," but a closer match is "The Kid" (1921), which tells a story of a mother who dies and her child faces hardship, though it does not specifically focus on foster care. Another possibility is "The Grapes of Wrath," which, while set during the Great Depression, explores themes of family separation and hardship. If you were looking for a specific title, please provide more details for clarity.