Available at Mises.org
Whatever Happened to Penny Candy was the book that introduced me - at age 38 - to Austrian Economics. I read the book after my wife bought it as an economics text for my oldest son. Penny Candy shook my neoclassical background to the core, in an evening nonetheless.
After reading the book, I searched the internet for "Austrian School of Economics" and found Mises.org.
The book is a great introduction to the free market for middleschoolers, highschoolers, and adults who haven't yet shed the statist influences of public education.
A truly excellent book!
Buy it for your children or buy an extra copy to give to your local library or friends.