Nagaya shinshiroku

In post-war Japan, a man brings a lost boy to his tenement. No one wants to take the child for even one night; finally, a sour widow, Tané, does. The next day, complaining, she takes the boy to his neighborhood and finds his father has gone to Tokyo; it seems the boy has been abandoned. Tané wants to leave him there, but he follows her home. The next morning he disappears fearing a scolding after wetting the bed. Tané realizes she likes having him there, searches for him, and keeps him when he's found that night. Within days, she considers him her son. - IMDb