The couple, both 43, announced their big news on Jan. 17, three weeks after the little girl was born to a gestational carrier at The Women's Hospital at Centennial Medical Center in their adopted hometown of Nashville.
Faith Margaret takes her middle name from Kidman's grandmother and her first from what her parents say they relied upon to fulfill their dream of expanding their family. "They never gave up faith they'd have another child together," says a friend of the couple. "They feel blessed."
The new arrival, who is the couple's biological child, joins big sister Sunday Rose, 2, and Kidman's kids from her marriage to Tom Cruise, Isabella, 18, and Connor, 15.
Kidman has spoken openly in the past about her struggles to conceive daughter Sunday, telling PEOPLE in 2009 that she and Urban hoped to have more children if they could: "We always say, 'If it's God's plan.' "
Now that the have added another daughter, says the friend, "they’re just thrilled."
For much more on the latest addition to Kidman and Urban's family, pick up issue of PEOPLE, on newsstands Friday