Not saying that this is what you're arguing, but - I wish it wasn't assumed that children are only able to understand simple concepts. Younger kids might find it hard to get through dense prose, buy that doesn't mean that the ideas therein couldn't be understood with appropriate presentation.

If you've a child with a deep interest in an area, you get to the point where you've devoured the children's literature on the subject and are left grasping for new material that will satisfy their thirst for new knowledge in a form they can read themselves.