New York, Oct 10 (IANS) Hollywood actress Angelina Jolie says she and her partner Brad Pitt are finding their newborn twins 'a challenge'.

In July, Jolie gave birth to twins - Knox and Vivienne - and confesses she and Pitt are often left exhausted.

Imdb.com quotes her saying: '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 - they have started resembling their famous parents.

'It's funny. Knox looks more like Brad and Viv (Vivienne) more like me. They're totally sweet. Knox is more the quiet one, very relaxed, while Viv is a little more aggressive and loud,' said Jolie.

Meanwhile, in the new W magazine, Jolie revealed that 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.