You really can't go wrong with any of the 4-stars that were listed. Independence Hall is on 6th Street, so definitely walkable from Penn's Landing. From there, you can walk to the Reading Terminal and City Hall. I'd take a cab to the Franklin Institute or the Art Museum, or you can catch one of the trolleys that take you around.
Remember, Ben Franklin is buried near Independence Hall and Betsy Ross's house is near his gravesite. If you're interested in an authentic Revolutionary-era dinner after your site-seeing, you can go to City Tavern on 2nd and Walnut. They serve venison, rabbit, duck, etc., from that period and they also serve "normal" dishes for the less adventurous. It is not inexpensive, though, especially if you're bringing kids since there is no kids' menu.
If you need advice about things to do, don't hesitate to ask. Oh, and check out the Convention Center's website. We stumbled upon a food trade show one year that was about $15 to enter and had aisle upon aisle of tasting stations. It was sponsored by the Food Network and Kitchenaid, called The Book and the Cook. Unfortunately, it was moved from center city to somewhere near Plymouth Meeting a few years ago. We went several years in a row until they moved it.