Mega Maggie Gyllenhaal

Gyllenhaal is lucky to have real help in the child-rearing endeavor. "Peter has been absolutely equal in terms of parenting," she says. "He really understands what it means to work until 5 in the morning, which I did the other day, or if I say, 'I need you to sit down and help me learn these lines,' or 'I need you to take Ramona.'" And it goes both ways: This past March, she dropped out of the marital dramedy The Private Lives of Pippa Lee when a new shooting schedule meant she would be apart for too long from Sarsgaard, who was in London shooting the coming-of-age movie An Education. She and Ramona joined him instead. "I loved being 'the wife,'" she says, "but if I didn't have my own work, it would be rough on me."

The couple has agreed that since Sarsgaard recently made two movies, it's her turn next, but in truth their choices will depend on whose agent calls first with a great part. "If suddenly Peter was offered the lead in a Scorcese movie," she says, "I'm sure we'd try to find a way to make it work."

Her brother, Jake, 3000 miles away in Los Angeles, is unavailable for babysitting duty, although Gyllenhaal says he's up to the job. "We lived with him in Los Angeles when Peter and Jake were making Rendition," she recalls. "Jake has a beautiful house, much nicer than a hotel. He's great with kids—it comes naturally to him. He really has that touch."

Jake, of course, is partnered up with Reese Witherspoon, who is freshly divorced and the mother of two. When I mention having seen a photo of them in The New York Post recently, Gyllenhaal grimaces. "We're so protective of our privacy and our family," she says. "The level of invasion is out of control. Jake has gotten more used to it than I have—he rolls with it better."

While most young actresses would leap at the chance to be the female lead in a mega studio movie, Gyllenhaal was cautious, interrogating director Christopher Nolan about the role of district attorney Rachel Dawes, previously played by Katie Holmes. "Maggie came to me with very strong ideas about the character and the changes she wanted to make," Nolan says.

But once she committed, Gyllenhaal didn't look back. "I immediately recognized that she was someone I could play with," Eckhart says. "We'd have our little improvisations before the scene, and she was always trying to get the last word in, and so was I. But as sexy and smart as she is, she's earthy as well. She'd bring her baby to the set, and she doesn't have any problems with doing what she has to do as a mother"—meaning, change diapers and breast-feed.

As for the sharp detour into popcorn flicks, Gyllenhaal's motivation is strategic. "There are 10 names that can get a movie made," she says. "I have respect for women like Cate Blanchett and Nicole Kidman and Kate Winslet." So what would it take for her to join those ranks? "I think it would take me being in a movie that made tons and tons of money." Perhaps The Dark Knight will be her Titanic—in the box-office sense, of course.

But there is no sense in which she was slumming in The Dark Knight. "It didn't in any way feel like a compromise," Gyllenhaal says. Citing the director and her roster of costars—Eckhart, Gary Oldman, Christian Bale, Michael Caine, Morgan Freeman—she adds, "it didn't feel like working on a comic-book movie."