Best reference books for children aged 3 to 12 years?

What are the best non-fiction books for children aged 3-12y? Did you have a reference book that you loved as much as a novel?

Which are the most beautiful (or weird/furry/ugly) children’s books?

Bring me your beautiful, ugly, weird, and furry books.

2016 School library update

I'm trying to help build a school library -- looking for brilliant book ideas.