The 227th Street Playground in Bronx Park, June 2015, showing the standard WPA comfort station. It seems that these once had windows, but now they are bricked up. If you read through the 1934-43 Parks Department press releases, you will see that during New Deal, every playground had a supervisor who organized activities, taught classes, and so on. I suspect that in smaller parks like this one, the supervisor had office, storage, and classroom space in these comfort station buildings.

The New Deal in NYC 1932-1943 | Frank da Cruz | fdc@columbia.edu