ARTHUR ASHE KIDS’ DAY: Pop stars JoJo and Gavin DeGraw will join tennis stars Andy Roddick, Serena Williams, Steffi Graf and other top players at the annual U.S. Open Arthur Ashe Kids’ Day. The interactive festival offers tennis clinics hosted by professional players and a stadium show. Tomorrow from 9 a.m. to 5 p.m. USTA National Tennis Center, Flushing Meadows Park, Queens; (888) 673-6849.