The immediate change that the child brings about in Silas was that he first thought that it was his little sister who died in childhood and that maybe God had sent her back. Upon thinking this, a lot of memories from his childhood began to rush through his head, touching all those emotions that he had buried in the past. He had made a point of forgetting his past life and whatever good or bad came out of his time in Lantern Yard. To him, that was a burnt past that he would never touch upon again.
However, when the child came all these suppressed memories came up and all the feelings he tried to bury surfaced. And he felt quite placid about it. It was as if the little girl had brought with her all the hope, love, feeling, and emotion that Silas had put away for years and years. All that change happened instantly as he stared at the child. It was a forgiving look into the past, and a hopeful look into the future.