You can blame -- or praise, if you insist -- YouTube for this concert pairing Greyson Chance and Cody Simpson, since it brought both barely pubescent teenagers to mainstream attention. Chance, of course, is the piano-playing, "Paparazzi"-covering teenage sensation now recording for Ellen DeGeneres's debut record label, while Simpson is an upstart Australian now signed to Atlantic Records. Talk about teenage idols. Thursday, April 28, at 7 p.m. Sixth & I Historic Synagogue. 600 I St. NW. Tickets are $25. Call 202-408-3100 or visit sixthandi.org.