I haven't run for or played a Child-Thing, so I can just help you with just the last two questions.
The PC might not be a human, but they can still have humanity. Keep in mind even NPC Wolfs are Grotesques, which are explicitly described as incredibly fucked up people - but still people and subject to the "Make everyone human" Principal.
The PC Wolf doesn't have to be going after the Child-Thing. The NPC Wolves are, but you can ask the Wolf PC "So why aren't you interested in hunting the Child-Thing?" Hell, there's nothing saying they can't be allies to the Child-Thing if that's the route the players go.