I'm going to have a look at the similarities and influences of Alice in Wonderland with Pans Labryinth. There seem to be quite a few, so this could be one of our main themes.
Lewis Carroll's story was based around a 'young female protagonist who enters an underground fantasy world in search of escape from the tensions of her home',
"The little girl descending holes (following creatures) is a deliberate reminder of Alice..., and of other girls in fantasy realms, such as Lucy in Narnia."
"The book presented to Ofelia by the fawn has blank pages until she looks at it in the enchanted space of the bathroom. The image of the girl in the book is clearly Alice crawling into the rabbit hole."
As Ofelia approaches the first task, she is dressed as Alice – as originally illustrated by Sir John Tenniel
(You mentioned this earlier Ethan)
On her hands and knees beneath the tree Ofelia/Alice feels oversized. The frog creature is like any number of creatures encountered by Alice in Wonderland.
Guillermo del Toro has cited Arthur Rackham’s later illustrations of Alice in Wonderland as an influence on the look of the film.
The faun judges Ofelia harshly, then fades away in the darkness like the Cheshire Cat in Alice.