The Return (1940)

Little Nikita, the son of polar scientist Sergei Ivanov, runs away from home with the intention of reaching the Arctic, where he believes his father works. The boy manages to reach Leningrad, where he ends up at the Arctic Institute. Sergei is tasked with returning the runaway home, but Nikita stubbornly hides his origins and the purpose of his escape. Soon, his grandmother arrives, and Ivanov learns that Nikita is his son. He writes a letter to his ex-wife and convinces her of the need to return to him. The couple reconciles, and, preparing for another expedition, Sergei promises his wife and young son that he will return to the mainland on time.