While the narrator does not make it clear until the final lines of the story that the child protagonist is deaf and mute, they foreshadow this fact throughout the story. For example, when the boy gets lost in the forest, he calls with "inarticulate cries" for his mother (foreshadowing that he is mute), and, as the wounded soldiers drag themselves through the forest, the narrator describes how this all happened “in silence profound, absolute” (foreshadowing that the boy is deaf).
Perhaps the most obvious example of foreshadowing is the following passage, in which the narrator describes all of the sounds of battle that the child was able to sleep through:
Their successive battalions, breaking into swarms and reforming in lines, had passed the child on every side — had almost trodden on him as he slept. The rustle and murmur of their march had not awakened him. Almost within a stone’s throw of where he lay they had fought a battle; but all unheard by him were the roar of the musketry, the shock of the cannon, “the thunder of the captains and the shouting.” He had slept through it all.
That the child was able to sleep soundly as hundreds of soldiers marched by him and then fought a full battle close by, featuring “the roar of the musketry, the shock of the cannon” and “the thunder of the […] shouting,” clearly foreshadows the fact that the boy is unable to hear.
It is only at the end of the story that readers can understand why the child was able to sleep through this scene and, also, why he's able to react positively to the presence of bloodied and wounded soldiers crawling through the woods after the fight. Because he can't hear the soldiers’ cries of pain and grief, he is able to hold onto his fantasy of war as a game, playing make-believe with the soldiers as they suffer (and even die) around him.
