History.com has a photo gallery of Pennsylvania for kids. This site from USHistory.org has a landing page on William Penn with a lot of links: Did your kids know that Penn did hard time in the Tower of London? This site also had a lot of printables and information on Pennsylvania as a state, as did this page from apples4theteacher. Page 48 in the STOW Activity Book has a coloring page of William Penn's statue that stands on top of Philadelphia's City Hall; FYI, the city was founded by Quakers.
If your kids are interested in the Quakers, here's an article written to a late elementary level that would be good for research purposes.
Note: Here you'll find more than a week's worth of elementary-level lesson plans on colonial America.