Jeanne Bendick, author of Archimedes and the Door of Science, explains some basic concepts regarding the universe in a surprisingly simple way (approximately 2nd grade reading level - short pages with large type). First she invites children to try to imagine how big the universe is (in terms of it being much, much bigger than other, more familiar things). The bulk of the book focuses on large distances and how they're measured and how people used to believe that the earth was at the center of the universe and remained motionless. The final page explains the big bang theory. For a controversial topic it is explained rather nice in terms of "How did the Universe begin? Nobody knows for sure, but here is what most scientists of today think." Although the big bang theory was first thought of by a Catholic priest (LeMaitre) who was trying to point toward something which God created, we all know that the big bang theory is often used to try to explain God away. Young children don't have much trouble with this when presented as it is in this book. After the book says "Suddenly, this object exploded with a big bang," you can ask your children, "If this is the way the Universe really did begin, then who made the explosion happen?" Chances are, they'll know the answer. :)