I think what it is and what it looks like are far less important than what it has done. Frankly I'm a bit alarmed at how quickly the fact that Cole habitually murdered children for years seems to be getting so easily brushed aside because of how it looks and what it might or might not be.
Hmm... I've actually read posts regarding this, and have been thinking about how to word it right... Here goes:
I don't brush it aside at all. What he did was horrific, no doubt. However, i would make the argument that he may not have realized what he was doing was wrong. Or, alternatively - what did it matter if it was? It filled a need, and there really wasn't any reason not to. It wasn't like he'd be punished. it wasn't like anyone would care. And I genuinely believe the moral implications of ending someone's life were at that time mostly beyond him. Not that all this makes it okay, but it does make it understandable.
Fast forward to his befriending Rhys. Suddenly there is someone who cares. Someone who will disapprove, and potentially punish him by not wanting anything to do with him anymore. Sure, that's not a good motivation to stop killing. But it's a motivation. Over the course of the novel, his friendship with Rhys leads him to want to be better. At first it's for selfish reasons, sure (I don't want Rhys to hate me), but I think that's a starting point for him to start thinking about what's right and what's wrong, and why he does things and why he shouldn't. He evolves, and he grows. By the end of the book, i think he's come a lot closer to becoming human (in the ideaological sense, not in the literal sense, since, well, you know...) and all that entails.
So, to sum it up, yes, he did something bad. But now he wants to be good. He wants to help others. I think that's worth giving him the opportunity to earn my trust.