Brad Pitt's youngest children didn't recognise him without a beard.

The 46-year-old actor - who raises six kids with partner Angelina Jolie - left two-year-old twins Knox and Vivienne confused when he returned home clean-shaven and brown-haired after a trip to the barbers to alter his appearance prior to starting work on his next movie 'Moneyball'.

A source said: "Knox and Vivienne were so young when Brad started growing his beard that they didn't know him any other way.

"After Brad got rid of his facial hair, Knox and Vivienne didn't recognise him.

"Brad kissed and hugged them when he left for the hairstylist, but when he came home three hours later with his hair cut, the grey dyed out and his face totally smooth, Knox and Vivienne ran away from him screaming. They ran up to Angelina, saying, 'Where's daddy? Who's that man?' "

However, the twins have now got used to their father's new look, and recently spent some quality time with him while Angelina travelled to Moscow and Japan with the couple's four oldest children - Maddox, Zahara, Pax and Shiloh - on a promotional tour for her new movie 'Salt'.

The source added to the National Enquirer magazine: "Angelina and Brad decided it would be best for the twins to stay behind.

"It's taken some time, but Knox and Vivienne are used to their smooth-shaven daddy."