Angelina Jolie has two daughters recovering from surgery

March 9 (UPI) -- Mom-of-six Angelina Jolie says she has two daughters that are recovering from surgery.

The 44-year-old actress and humanitarian praised her daughters' strength and bravery in an essay for Time published Sunday on International Women's Day.

Jolie has six children, Maddox, 18, Pax, 16, Zahara, 15, Shiloh, 13, and twins Knox and Vivienne, 11, with her ex-husband, actor Brad Pitt. She shared how Zahara and one of her younger daughters recently had surgery.

"I have spent the last two months in and out of surgeries with my eldest daughter, and days ago watched her younger sister go under the knife for a hip surgery," Jolie wrote.

"They know that I am writing this, because I respect their privacy and we discussed it together and they encouraged me to write," she said. "They understand that going through medical challenges and fighting to survive and heal is something to be proud of."

Jolie said her daughters have cared for and supported one another as her two daughters experience health issues.

"My youngest daughter studied the nurses with her sister, and then assisted the next time. I saw how all my girls so easily stopped everything and put each other first, and felt the joy of being of service to those they love," Jolie wrote.

"I also watched them face their fears with a resolute bravery. We all know that moment when no one else can help us, and all we can do is close our eyes and breathe. When only we can take the next step or breath through the pain, so we steady ourselves and do it," she said.

Jolie said her sons have been "supportive and sweet" toward their sisters, but also spoke about how girls are often expected to take care of others and have their worth defined by it.

"Little girls' softness, their openness and instinct to nurture and help others, must be appreciated and not abused," Jolie said. "We must do much more to protect them, in all societies; not only against the extreme ways girls' rights are often violated, but also the most subtle injustices and attitudes that so often go unnoticed or excused."

Jolie encouraged people to value and care for girls, saying that stronger and healthier girls are able to give more back to their family and community.

Jolie brought her five younger children to the Los Angeles premiere of Maleficent: Mistress of Evil in September. She shared at a press conference in October how being a mother "completely transformed" her.