Angelina & Brad Shop for Baby

04/12/2006 at 03:20 PM EDT

Before Angelina Jolie and Brad Pitt flew to Africa last week, the couple stocked up on baby stuff at a Paris boutique – including dresses, socks, a bonnet and a layette, an observer tells PEOPLE.

"We think it's a girl, but we're not 100-percent certain," the observer says he overheard Jolie say during the private shopping jaunt.

Still, the source tells PEOPLE that the actress also purchased a gray T-shirt with the word "boy" on it . . . "just in case." Besides, she said, "since I already have a boy and a girl, it doesn't really matter."

Besides the gender of the couple's baby, the other question is: Where in the world will their child be born? The globe-trotting pair arrived in the southwest African country of Namibia on April 4 with Maddox, 4, and Zahara, 15 months, and immediately holed up in a tiny, beachside lodge – with very tight security.

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Among their first adventures: visiting a game reserve. A local source tells PEOPLE that Jolie "fell in love with the country" when she filmed Beyond Borders there in 2002 and is "here for the birth of the child." (Another source says that the couple have a plane on constant standby should they change their minds.)

Although Pitt has recently checked out business properties in France, Italy and the Dominican Republic, back in L.A. three construction crews have been working around the clock to finish renovations on his Craftsman-style home.