"I have four children and will be studying the Civil War with my two oldest, boys who are 8 and 6 years old. We will mostly read the books together aloud; however, my 8 year old is a voracious reader so some longer chapter book recommendations for him will be helpful as well. Our family is involved in a small co-op and we may use some books there (again a group of boys from 6-10 years old). Picture books work well in that setting!"
For young children studying the Civil War we'd emphasize some biographies and good picture books. Here's a starting list (this is a huge interest in our area and so we have many shelves full of titles on this subject!):
Minty: A Story of Young Harriet Tubman by Alan Schroeder illustrated by Jerry Pinkney
Beautifully illustrated picture-book biography of Harriet Tubman.
Tom Jackson: Young Stonewall by Helen Monsell (Childhood of Famous Americans)
This is a "best-option" choice, since I don't generally prefer the COFA series (though children usually love them), but there isn't a Stonewall, and you must read about this godly Southern General, in my other favorite biography series (see below). There is Robert E. Lee, Ulysses S. Grant, Abraham Lincoln (and others) as well in this series.
Robert E. Lee: Hero of the South by Charles Graves (A Discovery Book)
I really like this series of biographies for younger readers. Each book starts with the heroheroine as a young boy/girl, but then the rest of the book focuses on their actual accomplishments. Of course there is a Lincoln biography in this series, as well as Grant and Douglass.
Jefferson Davis by Patricia Miles Martin (See and Read Biography)
A good series for very early readers. Also in this series are biographies of Frederick Douglass and Robert E. Lee.
The Story of Ulysses S. Grant by Jeannette Covert Nolan (A Signature Biography)
Signature biographies read like their historical fiction equivalents--We Were There books, but the main "character" is the subject of the biography. Your older son who loves chapter books will enjoy this. There is also a Robert E. Lee and an Abraham Lincoln in this series.
Gettysburg by MacKinlay Kantor (Landmark Book)
A must read-aloud for at least your older son. This is a Landmark that shouldn't be missed as it does an excellent job covering this momentous battle. Other Landmarks about the Civil War include Robert E. Lee and the Road of Honor and The Monitor and the Merrimac.
Gettysburg: Tad Lincoln's Story by F.N. Monjo
For your younger son if he doesn't listen to the Landmark. This story is told from the perspective of Lincoln's son.
Uncle Tom's Cabin: Young Folks' Edition abridged from Harriet Beecher Stowe
A well written retelling, published long ago, suitable for young children. A good introduction to such an important work, and issue leading up to the Civil War.
Follow the Drinking Gourd by Jeanette Winter
A Five in a Row picture book that tells the tale of the "drinking gourd" or Big Dipper that slaves followed on their underground railroad to freedom.
Who Owns the Sun by Stacy Chbosky
Written by a 14 year old, this Five in a Row picture book is the best introduction to the concept of slavery that we have read.
...If You Lived at the Time of the Civil War by Kay Moore
A simple introduction to life during the Civil War, for all walks of life on both sides of the Mason-Dixon line.
The Civil War by Fletcher Pratt
A well-illustrated overview of the entire War between the States.
We Were There When Grant Met Lee at Appomattox by Earl Schenck Miers
For your chapter book reader. He also may enjoy We Were There at Gettysburg as well. Fictional kids find themselves caught up in historical events.
Blow, Bugles, Blow by Merritt Parmalee Allen
This is a chapter book about a boy serving under General Sheridan, sympathetic with the Northern side, though respectful of his southern opponents.
Johnny Reb by Merritt Parmelee Allen
Another story by Allen, but this is from the Southern perspective.
Phantom of the Blockade by Stephen Meader
Meader also writes great historical fiction books for boys. We hope your older son likes this one!