Lovely piece of artwork. The style is great for a child's book.
The only thing that needs to be fixed is the shading of the shadows. Because of the angle of the sun, the shadows belonging to the fox and tree should be at a sharper left angle than it is right now. [My sister says that that is a common mistake a lot of people make when they do shadows.]
I also suggest that you add a bit of shading to the ground below the hill since they are curved. And the shadows on the hill should be long, too

Besides that, the drawing is quite excellent. Hat's off to you for it. >(^;^)<

[Hope this is a a good critique. First time doing one. D:]