Julianna Tex and Henry Benjamin were born April 14, according to the Dixie Chicks' Web site. Julianna weighed 6 pounds 10 ounces and Henry weighed 6 pounds 14 ounces.
"Babies and mom are all doing very well," the posting said.
Robison and her husband, Charlie, also have a 2 1/2-year-old son Gus.
"For those keeping track, the welcome arrival of Julianna and Henry into the Robison fold brings the Dixie Chicks' baby count to seven, including a set of twins each for sisters Emily and Martie," the Web site said.