In stave 2 of A Christmas Carol, the Ghost of Christmas Past takes Scrooge back to his childhood and specifically back to the school where Scrooge was a student. Before we meet the younger Scrooge, we first pass by other boys who are described as being "in great spirits," talking excitedly to one another so that the "fields were so full of merry music." The merriment and vitality of these boys serves to emphasize, by contrast, the sadness and loneliness of their peer, the young Scrooge.
When we meet the young Scrooge, he is described as a "solitary child, neglected by his friends." He is inside in the old school building, while all the other boys are outside, playing and enjoying the fresh air. It is clear that the young Scrooge was not an ordinary, happy child, but rather a sad and lonely one. This presentation of Scrooge as a sad and lonely child helps the reader to better understand and perhaps sympathize with the older Scrooge we met at the beginning of the story.
When the Ghost of Christmas past points the older Scrooge to the lonely image of his younger self, we see a boy on his own inside a classroom, sat at a desk and "intent upon his reading." Seeing his younger self, the older Scrooge feels pity for the "solitary child...all alone." He calls him a "poor boy" and cries at the sight of him. Seeing his former self, Scrooge wishes that he had been kinder to children in his own time.