(Cover) - EN Showbiz - Brad Pitt and Angelina Jolie have promised their daughter that Santa Claus will bring her a special toy if she stops sucking her thumb.

The Hollywood stars are concerned about how often six-year-old Zahara has her digit in her mouth. They don't want her to become too dependent on it as she gets older so are trying to make her stop now.

Zahara is keen to receive a Monster High Doll from Father Christmas, so the two stars have come up with a way to bargain with her.

"Zahara has been sucking less and less and when she can't resist the urge she crawls under her bed or hides out in her closet because she's scared Santa will see," a source told National Enquirer.

Monster High Dolls come dressed in ghoulish costumes and are being pitted as an alternative to Barbies.

Brad and Angelina are said to be delighted with how well Zahara is doing and realise she's making a major effort to stop her thumb sucking.

"They understand that Zahara's chronic thumb-sucking needs to end sooner than later," the source added. "And Zahara has risen to the challenge. With the way things are going, she's going to be a very happy girl on Christmas morning!"

Brad and Angelina are also parents to Maddox, ten, eight-year-old Pax, Shiloh, five, and three-year-old twins Knox and Vivienne. (C) Cover Media