Fundamental scarcities/impulses underlying the Child-Thing

For most of the playbooks, it's kind of clear what scarcities and impulses drive the characters: the Skinner is fueled by his beauty and fragility; the Driver, by her need for freedom; the Hocus, by their cult; etc. The Child-Thing seems kind of different: it's weird like the Brainer, but doesn't have the same access to the abyss of the human mind that the Brainer does.

To put it another way, most playbooks are set up in such a way as to be immediately relevant to the lives of the other PCs, but the Child-Thing seems to face inward to some extent.

How should I think about the Child-Thing and the group dynamics it incurs?

I ask this because one of my players has made a Child-Thing, and I'm worried about it being marginalized in the human politics. (Nobody has chosen to be a Wolf of the Maelstrom, if that matters.)

IMO, the Child-Thing is very much a creature of the maelstrom. It's fundamental scarcity/impulse stems from its desire to understand the human condition. To blend in. To belong. But it is so alien that that understanding and belonging may be unattainable.

If you want to keep the Child-Thing connected to the other PCs, lean into the idea that "the maelstroms's wolves are hunting you" by making the maelstrom's wolves just really not good for anyone. In some sense, having the Child-Thing in your game is a perfect excuse to add as much of a supernatural element to the setting as you like.

I think the Wolves are part of the Child-Thing specifically because it can lean towards being self-sufficient - you have moves that let you ignore the need to spend Barter and even fully heal yourself. But you're going to need help dealing with whatever the hell the Wolves are, because even if you can fend them off when they attack...what are you going to do when they hurt or kill the people you care about or need? The other PCs are going to be essential unless you want to be in hiding for the rest of your life, never showing affection to anyone the brief moments you go out in the world lest the Wolves go after them when they can't get you.

These are wonderful answers. The key, it seems, is not to bring the Child-Thing into the human politics, but the human politics into the Maelstrom.

I can confirm that everything above really applies in the real game, even just on its own.

One of my players took Child as a second character and without anything else, she immediately ran to other characters asking for help with The Bugs (= her perception of wolfs) which integrated her quickly (and weirdly) into the group and its dynamics.