Xiunan Park, located in Pudong near Disney, is one of the 36 new parks the city is opening or renovating this year as part of the "Outer Ring Green Belt" initiative to make the city greener.
It's also one of the more kid-friendly parks in the city, featuring a decent-sized playground, a children's train (20rmb, every 10-15 minutes), and a super cool "Fun Track" for kids to ride their bikes and scooters.
Also, you can sit anywhere on the grass and set up a tent.
It might not be worth the trek from Puxi, but it's a nice option if you live in the southwest of Pudong or happen to be near Disney.