Where are y'all staying? The Benjamin Franklin Parkway will mostly be closed for the 4th for the festivites. There is a concert later in the evening with Meghan Trainor and Jennifer Hudson. The Parkway will be packed from City Hall-ish to the Art Museum. Fireworks later in the night. The actual fireworks shoot off behind the museum. Might be able to snag a spot on the Schutkill River Trail just past Boathouse Row to see them.
https://welcomeamerica.com/ Old City has the Constitution Museum, Independence Hall, and Liberty Bell right on the same mall. The Museum of the American Revolution is new and also same area. Good area to walk around. Society Hill also nearby and nice area to walk around.
The Delaware River waterfront from about Market south towards South Street and specifically Spruce Street Harbor Park is a cool area to hang out if it's not too hot. Might be worth it to check out renting Segways.
Cheesesteaks: Steve's or Jim's are better and more convenient than Pat's or Geno's.
Franklin Institute is cool as is Mutter Museum if you're into more oddities.
Valley Forge is about a thirty to forty minute drive from Center City but may be worth it if you're into history. It's very pretty. I would recommend the Wissahickon Park if you're into either biking or hiking. Forbidden Drive and some of the trails are very nice. Chestnut Hill area is close and nice to sortof walk around and window shop/eat.
Philly is also an hour and a half from the Jersey Shore which you can visit for the day if so inclined.
Let me know if you have any other questions.