Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Earnest & Thoughtful
Your run-of-the-mill kids' book might be funny or goofy or wacky. But not The Velveteen Rabbit.
This story is all about love and friendship, so it's no surprise that the tone of the book is honest and reflective. Just take a gander at this lovely passage:
Weeks passed, and the little Rabbit grew very old and shabby, but the Boy loved him just as much. He loved him so hard that he loved all his whiskers off, and the pink lining to his ears turned grey, and his brown spots faded. He even began to lose his shape, and he scarcely looked like a rabbit any more, except to the Boy. To him he was always beautiful, and that was all that the little Rabbit cared about. He didn't mind how he looked to other people, because the nursery magic had made him Real, and when you are Real shabbiness doesn't matter. (51)
The language here is simple as the Rabbit thinks on his life with the Boy. He's actually pondering something pretty intense—what it means to age and change with someone you love—but he's meditating on it with remarkably clear and straightforward words.
Margery Williams isn't trying to sugarcoat anything here—the Velveteen Rabbit has lost some of his beauty. But she's emphasizing the joys of loving and being loved in return with a whole lot of candor. We almost wonder where else you could talk about a subject like this so simply outside of a children's book.