The recruits that come to the front are getting younger and younger. As Kat once took care of Paul and his friends, Paul tries to do his best for the new young recruits. Germany is desperate for soldiers so they don't train the new recruits very well. This cycle is repeated throughout the story.
“A surprise gas-attack carries off a lot of them. They have not yet learned what to do. We found one dug-out full of them, with blue heads and black lips. Some of them in a shell-hole took off their masks too soon; they did not know that the gas lies longest in the hollows; when they saw others on top without masks they pulled theirs off too and swallowed enough to scorch their lungs. Their condition is hopeless, they choke to death with hemorrhages and suffocation.”