MADDOX’S BIRTHDAY SURPRISE!

When Angelina Jolie brought her oldest son, Maddox, with her to LA Studios on Aug. 3, it wasn’t just to give him the chance to see his mom at work. Angie, 32, also wanted to take Mad away from the family’s Santa Barbara, Calif., home so that Brad Pitt, 43, could get the house ready for the action-packed weekend the couple had in store for their son’s 6th birthday reports Life & Style Weekly!

“Brad and Angelina were heavily involved in the preparations,� says an insider. “They mapped out and set up everything themselves.�

Guests started arriving at the oceanfront property while Angie and Maddox were away. “He didn’t know anything about the party,� says a Pitt family friend. “He thought he’d be staying in LA with Angelina while she worked.�

But the next day, Maddox got the surprise of his life: a party complete with an elaborate military-style game of Capture the Flag, ATV rides, a waterslide and a dinosaur-shaped cake!

That fearlessness was on full display during the two-day birthday bash. On Aug. 4, the gang — which included about eight other boys, including the children of Angie and Brad’s security team — motored around the property on ATVs. “Playing on them is Maddox’s favorite thing in the world,� says the Pitt family friend. “That was the main reason they had the party in Santa Barbara, so Maddox could ride around.�

But as much as Brad wants Maddox to have fun, he always puts the boy’s safety first. “Brad was very concerned about Maddox not getting hurt,� says the first insider. “He made sure Mad was wearing a helmet,� as well as long pants and a long-sleeve shirt.

The festivities continued at 10 a.m. on Aug. 5 — the day Maddox was born in 2001 — as Brad set up a waterslide. “It was huge!� says the first insider. “Brad made sure the plastic was good and wet before anyone went down. He even inflated some rafts.�

Meanwhile, “Angelina found a comfortable spot nearby where she could cozy up with Maddox when he wasn’t sliding down the hill,� says the insider.