You've probably heard of the Seven Wonders of the Ancient World. You know, the Great Pyramid of Giza, the Temple of Artemis… the list goes on. But for Arrietty and the other borrowers, the leg of a chair is as big as the Colossus of Rhodes, and a little patch of grass is as awe-inspiring as the Hanging Gardens of Babylon. As our tiny protagonists are awestruck by everyday objects, we realize that normal is relative; in The Borrowers, there's more than one way of viewing the world.
Arrietty is the most awestruck of all the characters because she's the most open-minded.
Kate is the most awestruck because she's so amazed, she won't let Mrs. May stop telling the story.