In the same chapter of Diana Athill's biography (see Bible post below), she recounts a conversation with a friend who bemoaned the proliferation of animals in children's books, specifically talking, clothes-wearing animals.
A quick glance at Logan's bookshelves confirms it: This Dinosaur Is So Big! (dinosaurs), That's Not My Puppy (dogs), Guess How Much I Love You (rabbits), The Very Hungry Caterpillar (you get the picture). Thomas the Tank Engine isn't an animal but neither is he a person (does anyone else find him a teensy bit creepy?). We're Going on a Bear Hunt, about a family of five, really centres on the bear, not the people. And in Not Now, Bernard, Bernard quickly gets eaten by the monster.
Athill argues that"children respond to animal protagonists because when very small what they need is not to discover and recognise 'real life', but to discover and recognise their own feelings." While learning about themselves is only one reason for reading to children, her point makes sense. The most obvious application is Eric Carle's From Head to Toe, where children are encouraged to mimic animal behaviours (it also serves as a good party trick, Logan has built up quite a repertoir).
The only real exception I can think of are the Charlie and Lola books, by Lauren Child. The protagonists are most definitely children, and aren't "drawn in such an unrealistic way that they might as well be animals", as Athill describes Postman Pat (!). The appeal here is that no adults encroach on the stories - not even partially, like Mammy in Tom and Jerry - and the dialogue is defiantly childlike (the Animals book includes a "biggish elephant" and a "very biggish whale", the Shapes book "squarish" and "triangley" shapes). They may teach basic realities, but they keep that teaching on a child's level rather than preaching from an adult's point of view.
All this reminds me of a friend's mother who refused to let her younger sibling watch The Land Before Time, not because the dinosaurs were speaking but because the film was about dinosaurs, and as all good Christians know, dinosaurs didn't really exist. So we're back to the Bible again. No more religion today, promise!