Are you looking for a way to teach your children about the Constitution? Check out the U.S. Constitution app available from MultiEducator, Inc. It's free! For the iPhone, iPod Touch and iPad.
On the same 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.