The "Monster" star, who became a first-time mother in March when she welcomed four-month-old boy Jackson, said she applied for it beforehand so that the child could travel with her around the globe during film promotions.
"Going through the adoption process, I knew when I was gonna have him come into my life so before I even had him, I had to start figuring out how to get a passport for him because I knew this tour was going to happen for Snow White and the Huntsman," she said.
The 36-year-old kicked off her promotional duties at the film's world premiere in London on May 14 and since then she has been to Spain, France, Germany, and Japan all with her new baby by her side.
"We came through customs in LA and the agent held his passport next to his face and looked at me like I was smuggling another child in. This passport is valid for five years so I can't imagine (what it's going to be like in a few years)... I mean, babies change every day."