Stern was born in Suwałki, present-day Poland (then part of the Russian Empire). During the First World War his mother fled the Germans with him and his brother David. They found refuge with her sister in Russia. When he was separated from his mother the 13-year-old Avraham earned his keep by carrying river water in Siberia. Eventually he stayed with an uncle in St. Petersburg before walking home to Poland. At the age of 18, Stern emigrated on his own to Palestine.