The "Big Little Lies" star and her family were in Paris for Sunday's 11th birthday, which Kidman, 52, marked with an Instagram photo of Sunday and her sister Faith, 8, in front of the famous clock at the Musee d'Orsay museum.
"Happy Birthday darling Sunday #Paris,'' Kidman wrote.
Kidman and Urban have been protective of their two daughters, rarely showing them in photos and often shielding their faces like in Kidman's Instagram post.
She also shared a cute photo of them in May, but kept their faces hidden as Kidman hugged them tight.
Kidman also has two adult children — Connor, 24, and Isabella, 26 — whom she and ex-husband Tom Cruise adopted during their 10-year marriage. She also has been very protective of their privacy over the years.
"I'm very private about all that," she told Australia's Who magazine of them last year. "I have to protect all those relationships."
Her young daughters with Urban also keep her grounded. She won two Emmys in 2017 for her performance in the first season of HBO's "Big Little Lies," but Sunday and Faith were not as impressed as everyone else.
"The great equalizer is showing the Emmys to Sunny and Faith," Kidman told TODAY at the time. "They don't want them. It's so funny. It's such a kid thing. Sunday was like, 'Mama, I know you said we could put it in our shelf but it won't fit. We have enough things on the shelf.'"