Angelina Jolie

Ask Angelina Jolie about her children and like any proud mother, she'll brag about them.

"They give me so much joy, and I want to make a better world for them," the Oscar-winning actress said in an interview that aired Tuesday on ABC's "Good Morning America."

Jolie has a 4-year-old son Maddox, who was adopted from Cambodia, and a daughter, Zahara, adopted this summer from Ethiopia.

When she brought Zahara home, "she was 6 months old and not 9 pounds," Jolie said. "Her skin, you could squeeze it, it stuck together. Like ― it was terrifying. Just to see the difference what food and the right kind of ― just a little bit of care takes.

"She's like ― she has gained 6 pounds. ... We are calling her chubby. She's, you know, she's just a totally different baby."

Jolie says Maddox loves being a big brother.

"He came to the orphanage. He saw where she was living, and he saw she needed care. Kids understand sadness and poverty and hunger."

Jolie was accompanied by Brad Pitt, her "Mr. & Mrs. Smith" co-star, when she went to Ethiopia in July to pick up Zahara. Rumors of Pitt and Jolie's off-screen relationship had been circulating for months.

She appeared on the ABC morning show the day before a new MTV documentary chronicling her trip to a village in Kenya with U.N. adviser and economist Jeffrey Sachs was scheduled to premiere.

"The Diary of Angelina Jolie & Dr. Jeffrey Sachs in Africa" was set to air Wednesday, coinciding with the opening of the U.N. summit in New York.

"Africa is beautiful, marvelous, smart people, strong people, strong country and has a potential to be so much," Jolie said. "I'd love to see Africa flourish. ... It's magnificent and it has so much hope, so much possibility."

The 30-year-old actress, who is a U.N. goodwill ambassador, said her children motivate her to continue her humanitarian work.

"I'm fortunate to do what I get to do to be here, to talk about these issues," she said.

"I'm just grateful every day that I have the chance."