[edrx]

"Cronopios and Famas", by Julio Cortázar - I read it for the first time when I was about 13 and for many years I reread at least once per year;

"Zen & The Art of Motorcycle Maintenance" (Robert M. Pirsig)

"The Sailor Who Fell from Grace with the Sea" (Yukio Mishima)

"The Yage Letters" (William Burroughs)

"The Old Ways" (Gary Snyder)

"Life and Death (Elementary Go Series #4)", by James Davies. Really - I studied that one very seriously.

Note: I answered just the "What book had a big impact on you as a child or teenager?" part, and I ignored that you are building a library for your children and asking for recommendations...