For a light read that is still fairly good for information, H.W. Crocker’s PIG to the Civil War is not bad. It might be a bit difficult for a 4th grader, but the PIG books are designed for a lower reading level.
I am not sure what type of report he needs to do. If it is a simple book report, then the PIG book is out. The Lee book would be more appropriate, though old.
She also wrote a similar book for Thomas J. Jackson, also good.