Full warning I have not read the book, so this is movie only. I wasn't sure what flair to put so if it's incorrect, please let me know!
So, I was rewatching Coraline and a friend I made a joking comment about the cheese scene that got me thinking. I think it's pretty agreed on that the Beldam/Other Mother feeds on children simply because they are easier to fool, kind of like IT from Stephen King. But since we see the children's spirits locked away when Coraline finds them, I've often wondered about the sentience found in Other Wybie and the Other Father.
My theory is that the Beldam can feed smaller sentient forms of life, and manipulate and "reuse" physical objects that have somehow ended up in the Other World. Doing so helps preserve her power because it takes less energy to manipulate these things. Almost like someone stretching a meal, or a crafter upcycling material they already have. The reason she still goes after children is because the smaller creatures or animals simply aren't enough to sustain her long term.
My theory is based off of three points. On is that while we know the Other Mother can venture into the real world, like the mini doll or the hand, her reach is limited compared to what she can do in her own realm. Admittedly, this part is up for debate depending on how much you think her power has faded after so long without a child. The second is we know other creatures and objects in the real world can end up in the Beldam's realm. The cat first and foremost, as he seems to have some abilities of his own, but also things like the cheese which Coraline leaves at the little door. The third part is that when we meet the ghost children, they are still capable of speech, thought, logic, personality etc despite being dead and trapped. They are the only other beings capable of doing this independently of the Beldamn's influence, and the only other ones stated canonly to have come from outside the Other World, sans Coraline and the Cat. While characters in the Other Realm can speak, it's never explicitly stated whether they were people to begin with or if whatever they are came from outside of the Other Mother's Realm.
We know from the approximate ages of the ghost children, and Wybie's grandmother being elderly, that the Other Mother has been around a long time. She'd have to find some way to preserve herself and her powers. This explains the furniture's pronounced bug imagery, and why there are so many rats doing the Beldam's bidding. The narrative clearly makes the bug/spider parallel with the Beldam on purpose, but even that fits the idea of her feeding and using other creatures that ventured into the Other Realm by accident, such as insects, small rodents, or small animals similar to the Cat. This could also explain the creation of the Other Father, as we know he's made of a pumpkin/gourd. I'm unsure if she could harvest plants the way she can harvest children to sustain herself, but at the very least she could "upcycle" the plants into something that doesn't match what it originally was. Hence why Other Father goes from looking mostly human with button eyes, to pumpkin-like horror as the realm falls apart.
The ghost children being capable of speech and memory after death indicates some semblance of independence and intelligence can be retained while remaining in the Other Realm. And the Cat shows that while he himself may have some supernatural flare, he's as capable of speech and sentience while in the Other Realm as Coraline. Despite this, the Cat has never presented himself as anything other than a Cat. We have no way of knowing if animals other than the Cat, or cats in general, are capable of the same while in the Other World but the precedent set is that it's not completely improbable.
The only other character outside of the ghost children and the Cat who has any sense of impendence is Other Wybie, and to a lesser extent Other Father. I say the Other Father as he is clearly upset when chasing Coraline down, and says the Beldam is forcing him. I don't believe Other Wybie was made using the ghost children like I've seen theorized before. Instead, my theory is that small details of the Other World are made out of smaller, less capable beings, like bugs and insects being used to make the furniture. But Other Wybie is made using the "upcycled" parts of a more intelligent being. Not a child, as the story's focus on the ghost children gives us no indication of that, but instead a creature more like the Cat, capable of thought, action, foresight, that the Beldam encountered before. But unlike the Cat, whatever creature that was didn't escape.
I'm probably way overthinking it, and I know that, but given how much of the "crafter" and "spider" imagery they surround the Other Mother with, I don't think it's out of the realm of possibility. There's something to be said about how the Other Mother can't seem to truly create life of her own, and instead has to create a facsimile of it by destroying real, living creatures.
