Check out the new playground that has been proposed for lower Manhattan. It is designed to be interactive and spur imagination.
When I taught 5th grade, my students once helped build a playground at a local science museum. Google helped me find the designer of that project, Tom Rockwell, and several others projects that his team has done. Cool stuff!
I also had a recent conversation with the Trust for Public Land about their efforts to preserve and create green spaces, including parks near public schools. Nature makes its own playground!