Whenever we go down to Miami Beach for the day, we try to go to this park. It is really beautiful since it's right by the beach. The playground area has a climbing structure with slides, there's a swingset and also a monkey bars and tire swing. There's also tons of sand (sand box or au natural via the beach). The only problem with this playground is that there is no shade protection-- a bummer in the hot Miami sun. The best times to go is on overcast days (still use sunscreen!).
There is a public restroom right next to the playground (which looks a little skeevy from the outside, so I've never used it) There's also a shower nearby, since it's by the beach, which is great for rincing off sandy hands and feet!