The Underland Chronicles/Headscratchers

Size...
 * Given the very blatant Down the Rabbit Hole description in book one I just went with it. Humans got smaller, then for whatever reason nothing else did. (Added to the implications that the rats sometimes went to the overland. Then Ripred mentions reading in a library, I believe) and some in the Undlerland may be the same ones above... Rereading the series I realize that can't be right because when they come up from sewers and such everyone is the right size, every damn time. WTF?
 * The humans don't shrink but because of the lack of predators (or some reason the science is kind of iffy) the animals that would live in the underland such as bats, rats, cockroaches etc. have all grown to about human size.

How is this in Children's Literature?
 * Book one, fine. Book two, fine. Book three is iffy with the nightmare fuel but once the graphic mause holocoust starts spaninng CHAPTERS of description, it should get something to warn the parents.
 * Esp. taking into consideration Harry Potter can be found in Children's Lit along with Teen, Young Adult and Adult in most bigger libraries. Why not Underland? It seems like a huge factor into why it is so underrated.