Hmmmm, eink readers are not good for color books or books with images. Zooming features are kind of rudimentary and basic.
If it was me, I would buy any of the less expensive 7 inch Android tablets. They provide zooming capabilities and color plus are less boring to use for any kid under 10. However, at that age, a regular paper book would be a richer experience in my opinion.
But yeah, go for a tablet, a Galaxy Tab or Kindle Fire. Or similar Android device.