Comment by Yaoi Whispers on The Hunter Wants to Live Quietly - Chapter 49

@Yaoi Whispers I believe it's because he's convinced that the child is already dead. He's been blaming himself for the death all this time so it's unlikely for him to be looking among the living for him. 

Additionally, he never saw what the boy looked like. His hair and skin was all destroyed from the poison and he also couldn't talk. If the boy was alive, I'd imagine he'd be looking for someone severely disfigured.