We have a great park just down the street (about a block and a half), but the street is great and it's right outside. Maybe 10 cars per day travel our street. Besides, the street is paved for bikes and rollerskates. The park is, of course, not. Also, it's easier to keep tabs on the kids right out the front door than it is when they're unsupervised down at the park.
But, yes, they also play at the park. They all run all over the damned place -- because it's a safe place and, culturally, the people living in the neighborhood have a high degree of trust and look out for one another. It's very difficult to replicate that in high density urban developments with the attendant problems those areas recruit (e.g., crime, homelessness, etc.).