For my first pick, under the category of
Children's Literature, jammies' Fahrenheit 451 would like to pick the duology
Alice's Adventure's in Wonderland and
Through the Looking Glass by Lewis Carroll.
Using absurdity and a delightful kind of logic which exactly mirrors that of children, the books skilfully exploit many of the conventions now claimed by modern fantasy, and read as well today as they did when published over 140 years ago. The heroine, Alice, undergoes a series of experiences featuring iconic characters such as the Mad Hatter, the Cheshire Cat, the Red Queen, and the White Rabbit, as well as my personal favorite, the Jabberwock ("the jaws that bite, the claws that catch!").
The most marvelous thing about the books is Alice herself; no matter what ridiculous situation she is put into, she copes, and copes well, accepting her madcap companions on their own terms but expressing her own opinions in a forthright yet polite way when she feels there is a need. She perfectly expresses an ideal Child: intelligent, curious, resourceful, imaginative, and sensible. She is also portrayed a person in her own right, which is a very modern concept that had little precedent at the time (
Oliver Twist (1838) was the first novel in English to feature a child protaganist).
The two books have never gone out of print, and deserve the clichéd adjective "timeless" far more than many similarly designated works of adult literature. Best of all, they are also freely available on the web, being from a time before it was felt necessary to have copyrights for the convenience of corporations rather than readers.