Dad Brad, mom Angelina, brother Pax, 6, and sisters Zahara, 5, and Shiloh, 4, joined Maddox and friends for a private party at Go Kart World in Carson, Calif.
"Brad and Angie rented the whole park, and it was closed down to the public to make sure that Maddox and his friends would be able to have a fun party in private," a source tells PEOPLE. "Maddox was very excited about his party and spent a lot of time racing his friends in the kiddy karts on the Mini Indy Track. The kids had the best time, and Maddox even got a trophy at the end of the party for being such a good racer."
The large group of children and adults had the facility all to themselves for two hours and spent the morning racing around the track, snacking on pizza and celebrating Maddox with a personalized birthday cake.
Although Maddox was the man of the hour, he wasn't alone in enjoying the ride at Go Kart World. In the past, such celebrities as Kate Hudson, Owen Wilson, Demi Moore, Ashton Kutcher and David Beckham have been there and jumped behind the wheel.
"Brad and Angie were wonderful hosts and make sure all the guests had the best time," the source said. "They acted very happy and relaxed together. Their other children also seemed to enjoy the racetrack and the party."