The American Civil War is the most studied and written about event in human history. It’s estimated that over 60,000 books have been written about the war. Dozens of books are being published every year including books geared toward young readers.
To get a feel for how many books have been written about that era check out this massive list: Bibliography of the Civil War (Wikipedia)
Civil War Books for Kids
More In Depth Reading
While many of these books are written for older readers, young readers will find a number of them interesting and worthwhile reading.
The Reading Lists website The Best Books on the America Civil War
From the Civil War Monitor- Historians pick The Best Civil War Books of All Time