I think that Frost creates a real sense of tragedy in the family's reaction to the death of the boy. The child's death is tragic, but it is not tragedy in that it is more of a chance, sad chance, occurrence. The reaction of the family takes time and there is a certain tragic reflection of how "life goes on" and there is little else to gain from mourning. The business of working on the farm continues, money to be made, and toil needed. It seems tragic to me because the grind of the work machine literally killed the boy and symbolically seems to be killing of the boy's memory. In this, I sense that there is a tragic dimension to the poem, something brought out even more by the abrupt end to the poem. There is little to indicate why the family has chosen to adopt such a perspective regarding the boy's death. However, the reality is that the boy's death is something looked beyond after a while, suggesting that even in memory, he is no longer of any value to the family. He realized this himself when he pleads to not lose his arm, almost foreshadowing his own uselessness to the family and when it becomes realized, the tragic condition in the poem presents itself.