He made it out to the Aryan side and joined another work detail, but those workers, too, were taken at gunpoint to the Umschlagplatz and put aboard a train. When the train was stalled, Mr. Milchberg managed to break the bars of a car window and scramble out, roll into a ditch and flee.

“To tell you the truth, I never thought much,” Mr. Milchberg said in a 2013 interview, trying to explain his daring resourcefulness. “If I had to do something, I did it. I didn’t have time to analyze it.”

He took a series of jobs that allowed him to move between the Jewish ghetto and the outside world, and he smuggled in food. While they were loading coal for a railway, his mother’s brother, the family’s only other survivor, put him in touch with rebel fighters. Not yet 16, Mr. Milchberg, according to the Ziemian memoir, smuggled guns to the ghetto in hollowed loaves, twice by spiriting through the sewers.

For several weeks in April and May 1943, as the last remnants of the ghetto were being “liquidated,” the fighters, armed with guns, grenades and firebombs, staged a quixotic revolt in what became known as the Warsaw Ghetto Uprising, a milestone of Jewish resistance. Mr. Milchberg, who had visited his uncle for Passover but did not actually fight in the uprising, was rounded up and put aboard a train to the Poniatowa camp. But when the group was switched to another train, he mingled with a crowd of Polish boys selling water and escaped.

He made it back to Warsaw’s Aryan side, but he badly injured his leg while running from a gendarme. He managed to persuade a Polish doctor he had known before the war to treat him. He ran into some youths he had met before, who were now hanging out with the cigarette sellers of Three Crosses Square, and joined the clique. The boys had nicknames like Conky, Hoppy, Toothy and Frenchy.

According to Mr. Milchberg’s son, surviving meant balancing “extreme fear and extreme hubris.” And indeed, some boys perished. The boy known as Frenchy was flattered by the attention of an SS man, thinking that might be an advantage, but for reasons they never learned, Frenchy was taken to the Gestapo and never heard from. Fearing that Frenchy might expose them all, the cigarette sellers scattered and went their own ways until the Soviet Army liberated the city.

In 1945, Mr. Milchberg made his way to Czechoslovakia, then Austria, then to a camp for displaced people in occupied Germany, where he learned watchmaking, his lifelong occupation. In 1947 Canada allowed 1,000 children to immigrate, and he became one of three cigarette sellers who settled there, while most went to Israel.