There is a small playground here at the Rosa Parks Senior Center on the east side of the complex at Golden Gate Ave. and Buchanan St. The playground has some nice landscaping surrounding it which adds to the ambiance.
This playground is part of the Buchanan Street Mall. You'll find more info on this pedestrian walkway at its ParkScan page (the link is below).
Additional Info
Muni access:
5-Fulton -- McAllister and Webster; walk one block east to Buchanan and a block north to Golden Gate Ave.
22-Fillmore -- Fillmore and McAllister; walk two blocks east to Buchanan and a block north to Golden Gate Ave.
31-Balboa -- Eddy and Buchanan; walk 1.5 blocks south on Buchanan (it's a pedestrian mall) to the playground at Rosa Parks Senior Center (you'll pass by one at Turk as well).
Buchanan Street Mall ParkScan page: http://www.parkscan.org/parks?parkId=78