For you history buffs, check out the history apps available from MultiEducator, Inc. I don't have the Civil War one, but it looks very interesting. I do have the Constitution app. Everyone should buy this and read it. It's free!
On that note, if you'd like to explain the Constitution to your children, I've found a workbook that I recommend to educators that will help - Our Living Constitution, Then and Now. It breaks the Constitution down point by point and "interprets" it in everyday language (the Founders of our country spoke a bit differently than we do today!). These two items are great resources to use to learn more about our Constitution and government.