I'm starting an Apocalypse World 2nd Edition campaign and one of my players wants to be the Child-Thing from the extended playbooks. In the playbook it mentions the Wolves of the Maelstrom and they said they couldn't find any reference to the wolves in the rules, and neither could I. So are there any rules, guidelines, or explanations somewhere that I've missed? Or are they intentionally vague and are just malevolent antagonists left for us to devise completely?

Thanks for any help!