The Jolie-Pitt clan knows how to party.  Brad and Angie hosted a belated birthday bash for Maddox Saturday morning at Go Kart World, and only RadarOnline.com has all the details.

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Maddox, who turned nine on Thursday, was the star of the day.  We're told his brother Pax and sisters Zahara and Shiloh were there for the party along with about two dozen other kids.

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