Another must see attraction in Springfield is the Lincoln Presidential Museum & Library (although I've never ventured in the library part of the complex). It covers Lincoln's life. I think it is very family friendly. My oldest was the only one of my kids to tour it and one of his favorite parts was the life sized dioramas. Though to some degree you can see he was a little freaked out when one could stand next to the wax figures.
Across the street at the depot museum (not the depot Lincoln departed from) there was a display of items from the recent Spielberg film Lincoln. Compare this version of Lincoln's cabinet meeting to the museum's version a few pictures above. It was only a couple of extra dollars to add this to the presidental museum ticket so we did. I don't think I'd tour this one again, once was enough, but would return to the presidental musuem again (in fact this was my second visit).
And here is the depot with yet another Lincoln statue. I bet we saw close to 3 dozen Lincoln statues on the trip.