I could not find an instance where Edek was sent to a "Warsaw" camp - I'm wondering if you might mean the "Warthe" camp, a camp in the nearby city of Posen for victims of tuberculosis, where Edek was sent at the war's end.
Peasants had been forbidden to sell food to anyone but the Nazis in Warsaw during the war, but "with the help of the older children they smuggled it to the towns and sold it to the Poles on the black market" anyway (Chapter 7). Edek became a skillful and daring member of one of these smuggling rings when the children were separated from their parents, but was eventually caught and sent to a forced labor camp in Germany, where he worked for two years. He managed to escape and return to Warsaw by hiding under a truck, but this escapade, coupled with the deprivation and abuse he suffered in the work camp, took a physical toll on Edek, and he contracted tuberculosis. In the immediate aftermath of the war, Edek ended up at a transit camp in Posen, from which he was sent to Warthe because of his illness. Always wary of being confined, Edek refused the help offered him at Warthe, and despite his poor health again struck out on his own. He managed to get to the village of Kolina, and there, just by chance, was reunited with his siblings.