Credit: ISM/Stefan/Flynetpictures; Sasha/

Beach blanket bingo...with Brangelina!

Back in the states after months in Venice, Italy, Brad Pitt and Angelina Jolie kicked off the holiday weekend Saturday at a pal's private beach party in Malibu, Calif. Joining the couple for the shindig were two eldest sons Maddox, 8, and Pax, 6. (Zahara, 5, Shiloh, 4, and twins Vivienne and Knox, 22 months, stayed behind.)

Quaffing a margarita, Pitt, 46, chatted with pals on the beachside deck, with Jolie, 34, drinking white wine beside him.

"Brad was very affectionate," a witness tells "He put his arm on Angie's wrist and was always rubbing her back or resting his hand on her shoulder."

Maddox and Pax, meanwhile, hit the surf on boogie boards. "Brad and Angelina were watching and pointing with big smiles on their faces," the observer says. "At one point, Pax was packing sand between his hands to make a ball and then throwing it as far as he could." The two buddies "liked trying to outdo one another."

And while their famous parents watched their fun from afar, the celeb kids "seemed independent and did their own thing without ever having to check in with their parents."

PHOTOS: More pix of Brad, Angelina and the boys' beach party at PopSugar

"Brad and Angelina seemed very trusting of their boys [and] wrapped up with each other," the witness adds. "They were having a good time relaxing and enjoying the great weather."