Superstar parents Angelina Jolie and Brad Pitt are finding their newborn twins "a challenge." In June the couple added Knox and Vivienne to their brood of four, and Jolie confesses she and her partner Pitt are often left exhausted.

She tells the German edition of Vanity Fair, "We're exhausted a lot, because it's twice as hard with two babies than with one."

But she insists the thrill of raising twins, makes the hard work worthwhile: "It's twice as much fun, too. When you look at them, it's like they were made for each other. They smile at each other, sniff each other, touch each other. It's just beautiful."

And the tots are already showing their different personalities - and have started resembling their famous parents: "It's funny. Knox looks more like Brad and Viv more like me. They're totally sweet. Knox is more the quiet one, very relaxed, while Viv is a little more aggressive and loud."

Meanwhile, in the new W magazine, Jolie reveals she and Pitt recently hired their first part-time live-in helper because they were going "loopy" trying to find time for all their kids.

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(This news article provided by World Entertainment News Network)