I also like the head in the middle better. It has a very surreal feeling, reminds me a bit of the Oryx and Crake book cover. I would suggest brightening your image up a bit. Right now everything is really dark, even the stars. They should be glowing, right? Play with the levels and colors a little to see what you like. I also really like the scarf dissolving into stars, it's a nice touch.
I guess the only other thing I would consider is who your audience is. I really like the image, but it has a fine-arts feel to it that seems more for adults. I think children tend to identify more with faces. I'm not an expert on children's books though, so take it with a grain of salt.