Public pools: check. Water slides: check. A spray park: check. Baseball and softball batting cages: check. Miniature golf: check. Leisurely hiking trails: check. Picnic grounds: check. Bocce ball pits: check. Multiple playgrounds: check. Upton Hill Regional Park, a naturally wooded urban park straddling Arlington and Fairfax counties, and its Ocean Dunes Waterpark hit all the high notes for family summer fun. Avoid the big weekend crowds and take a day off work to give the kids a midweek treat instead.