Kozak is the daughter of wealthy Jewish parents, Bronislawa (Landau) and Dawid Kozak, in the Polish town of Częstochowa, with a Jewish population of about 40,000 in 1939, or a quarter of its population. In 1939 when the Germans took control, the Kozaks' factory was commandeered and transformed into a munitions plant. In the town, an estimated 2,000 Jews were murdered by Germans on the spot and another 40,000 transported to the gas chambers at the Treblinka extermination camp. At some point Polish nuns in a convent took the Kozaks in and hid them from the Germans. Marion refuses to divulge where or when this took place. She also credits the "kindness and generosity of acquaintances in Warsaw" for her survival. She was also known as Maria. In the only official version of events, a biography of her husband Ralph Miliband written by a family friend, Michael Newman states that: "For the rest of the war Marion, Hadassa and their mother had been in constant danger and owed their lives to several brave people, Jewish and non-Jewish, many of whom were themselves killed."