Angelina Jolie's toughest critics? Her six kids with Brad Pitt.
The actress, who voices Master Tigress in Kung Fu Panda 2 (in theaters May 26) tells USA Today that her large brood -- including Maddox, 9, Pax, 7, Zahara, 6, Shiloh, 4, and twins Knox and Vivienne, 2 -- became "part agents, part managers" on set.
"They'll sit in a room and say, 'That's just not funny,'" Jolie, 35, says, adding that their fresh opinions "keep you competitive, even if they think Jack Black is always cooler than mom."
"You know, when you hear your own voice, you can find it quite boring and uninteresting," she explains. "Suddenly, you get very shy that your voice is not enough, because I'm not musical and I don't know my voice."
To gain confidence, Jolie looked to Black, 41, for support. "I was crazy about him. I had seen him in everything he'd done, but what I really knew him for was music," she says. "I don't have musical talent, so I always thought it was really cool that he could be an actor to a lot of us but equally a rock star."
Jolie's nerves came back again when she and Pitt, 47, took the children to DreamWorks studios to see a rough cut of the film.
"I wondered how they'd respond to the themes of the film," she says, noting that she and Pitt were "sensitive to see if there was going to be a big discussion that night about adoption and orphanages."
Fortunately, there wasn't. "But that's because we talk about those issues at my house all the time, very openly," she asserts. "We've had those discussions so often, they're such happy, wonderful discussions."
"We've got kids of all ages," Jolie continues. "So we joked that we had our own focus group."