Marysia Rozenszajn was born on June 19, 1941 in Białystok, at that time part of Soviet-occupied Poland; her parents Izak Rozenszajn and Bela Kaufman Rozenszajn were from Warsaw, but had moved to Białystok to escape the Nazis. Her father died four days after her birth, from the initial bombings of the Battle of Białystok–Minsk. After this battle, Nazi Germany took over eastern Poland and set up the Białystok Ghetto to confine the Jews of Białystok, including Rozenszajn and her mother.