Everybody Knows Kadkin (1977)

Original title: Кадкина всякий знает

The returning soldier Kuzma Kadkin on the train tells how well he lived before the war, and that everyone in the area knows him. An accidental fellow traveler, a young mother, leaves her child, a one and a half year old boy, Kadkin, to run away at the junction for water, but lags behind the train. Kuzma has no choice but to bring the baby home...