Despite all his efforts to keep his son safe, Guido unwittingly tells his son to go to the gas chamber:
Giosué: Daddy, I cannot find any of the other kids, and a lady came telling me to take a shower.
Guido: That's a good idea. You go take a shower.
Giosué: No!
Guido: Go take a shower!
Giosué: No!
Given that we only see Giosué when the camp is liberated, all the other inmates we saw during the course of the film were probably killed when the camp was liquidated.
At the end, Giosué has a voice-over as an adult stating that he lives his life appreciating his father's sacrifice. While heartwarming, this means he had realized the Frozen-In-Time horrors his father did everything to protect him from. He would grow up experiencing from Fridge Horror to Fridge Horror, connecting the horrifying dots, especially as his mother will no doubt explain it, and there will be a variety of sources explaining what happened in the Holocaust.