Izaak Kornblum came from a non-religious Jewish family. His father was a writer. Izaak’s mother died when he was three years old. He grew up in Warsaw with his father, stepmother, and half-brother. In 1940 they had to move into the ghetto, which was repeatedly raided. To avoid deportation, the family hid or bribed Jewish police officers. In 1942, however, Izaak’s stepmother was deported; his half-brother Borus was then smuggled out of the ghetto. Izaak Kornblum also escaped from the ghetto in 1943.
Using forged identity papers in the name of Wacław Bartkowiak, Kornblum looked for a place to stay. He eventually found work as a shepherd with Stanisław Śliwowski near Białystok. He received food and a place to sleep in the barn in return. Śliwowski learned that Kornblum was Jewish, but did not betray him. Fearing denunciation, he arranged for the young man to stay elsewhere. Kornblum hid in a forest with six other Jews. In the fall of 1944, he was discovered by a Wehrmacht soldier and arrested. He managed to escape. In 1945 Kornblum found his half-brother Borus and they were reunited.