From the text:
But there was another reason. I think we reminded them of what peace was like, we boys of sixteen. We were registered with no draft board, we had taken no physical examinations. No one had ever tested us for hernia or color blindness. Trick knees and punctured eardrums were minor complaints and not yet disabilities which would separate a few from the fate of the rest. We were careless and wild, and I suppose we could be thought of as a sign of the life the war was being fought to preserve. Anyway, they were more indulgent toward us than at any other time; they snapped at the heels of the seniors, driving and molding and arming them for the war. They noticed our games tolerantly. We reminded them of what peace was like, of lives which were not bound up with destruction.