On Saturday, April 18, the annual Street Games festival will introduce the Wii generation to activities their elders excelled at: stickball, box ball, skelly, roller-skating, and wall ball, among others. There will be live music, mostly of Motown vintage, and prizes for the most authentic Welcome Back, Kotter–era outfits. If kids would rather watch than play games, the Emperor’s Stickball League will be giving demos. Free, 11 a.m. to 4 p.m., at Thomas Jefferson Park (First Ave. at 111th St.).