Sara Singleton races her son Graham down the slide at Chestnut Hills Park on a sunny morning. In the background of the “big kid” part of the park is a long, blue curving slide flanked by a swing set. This newly- renovated park on Harrison Street in Arlington also has a large sandpit complete with five-year-old size bulldozers surrounded by wooden benches, as well as crawl through orange caterpillars, a Chestnut Hill yellow school bus with seats for two drivers and a drinking fountain when kids decide to take a short break.