Philadelphia International Airport is a good, organized, safe airport. Our family of five has had good experiences with our flights to and from there over the years. My oldest daughter flew on her first airplane at age four. She drew a picture and wrote a story, which ended up being published in the local newspaper.
Last year we traveled from Tampa to Philadelphia for a wedding. Our flight went well. We were a little disappointed to find that Tampa International Airport offered FREE internet for our laptops while waiting, while Philadelphia did not.
The Philadelphia airport is composed of many different concourses. It is important to know which concourse you are departing from in order to park in the right section. I suggest off airport parking at Wallypark. It is right next to the airport, the shuttles are fast, and it is cheaper that on-airport parking.
If you are flying to Philadelphia, I guess it really doesn't matter what I think about this airport because you are going to be there anyway. However, if you have to have a layover somewhere, this is a great option. There are lots of different food choices to please the entire family. There is a kids play area that is sponsored by the Please Touch Museum that allows kids to blow off steam before getting on a flight. I didn't pay attention to which terminal we were in, but the bathrooms were amazing. Every single stall in the women's bathroom was roomy and had it's own baby changing station! This may not seem like much, but when traveling with multiple children, sometimes it's the little things that make all the difference.