One change in the boys is evident right away: Paul and his friends are not at all ashamed to defecate in front of each other. During basic training, they were all embarrassed about using general latrines, but at the front they all sit in a semicircle on portable privies, and it is one of the most enjoyable aspects of their day:
We feel ourselves for the time being better off than in any palatial white-tiled "convenience." There it can only be hygenic, here it is beautiful.
While on the surface this may seem funny, it is only one way in which Paul and his comrades have lost their innocence. Indeed, they are, as Paul says at the end of the first chapter, the war has made them "old folk" despite their age. Another way in which this is evidenced is the gulf between them and the people at home, particularly Kantorek, their old ultranationalistic schoolmaster. Everything of their old life is now destroyed, according to Paul, and it is worse for the young men than for the older soldiers, who have families and jobs at home when the war is over:
We young men of twenty...have only our parents, and some, perhaps, a girl...The war swept us away. For the others, the older men, it is but an interruption. They are able to think beyond it. We, however, have been gripped by it, and do not know what the end will be.
They have become more callous to death, as evidenced by Muller's reaction to Franz Kemmerich's amputation and subsequent death: he is saddened, but also wants to ensure that he secures his boots, which are no longer of use to his friend. Above all, they realize that everything they have been taught in school is no longer of use to them.
We remember mighty little of all that rubbish. Anyway, it has never been the slightest use to us. At school nobody ever taught us how to light a cigarette in a storm of rain, nor how a fire could be made with wet wood--nor that it is best to stick a bayonet in the belly because there it doesn't get jammed, as it does in the ribs.
War has permanently destroyed their youth, and Paul makes it clear that even the survivors of the conflict have been lost.