In the spirit of the BeeGees, the Jonas Brothers, and Hanson—all well-coiffed trios of brothers—Cardinal Sons arrive at the Kennedy Center’s Millennium Stage bearing tight pants, sunny lyrics, and killer three-part harmonies. The Jackson, Miss.–bred group consists of siblings John, Joe, and Dave Shirley, and despite their deeply southern roots, their sound recalls West Coast indie pop more than rollicking country tunes. Consider the video for their latest single, “Day of Summer”: All three Shirleys stroll through a park while neon shapes flash in the background. “Awaken late and taste the day of summer,” the trio croons. Their lyrics don’t delve much deeper than sleeping late and soaking in the sun, but for a lazy August Monday, those bright sentiments feel just about right. Cardinal Sons perform at 6 p.m. at the Kennedy Center Millennium Stage, 2700 F St. NW. Free. (202) 467-4600. kennedy-center.org.