There are a ton of cool playgrounds for kids. My choices would be:
Clark Park - This park is on Chester Avenue & 43rd Street. There are swings and jungle gym sets for toddlers and sets for bigger kids. The diversity of cultures, races, and religions is just amazing. And there is always a festival, drum circle, or random soccer game going on. It's a very beautiful place to take children.
Penn Treaty - It's on Delaware Avenue and is a great place for families. There's tons of space for the kids and a nice size playground area. It's right near the water so it adds to the experience.
These are the two my children love the most. However, because Philadelphia has one of the largest inner city parks in the world there are gems all over that kids give a thumbs up to.
