Preston and Jayden celebrate with their family – including cousin Maddie Briann – in L.A.

By Brian Orloff and Pernilla Cedenheim
Updated September 13, 2008 10:40 PM
Credit: Starzlife; INF (inset)

Britney Spears revved up the celebration for sons Preston and Jayden on Saturday, throwing her sons a joint car and truck-themed birthday bash in Los Angeles.

And the party was truly a family affair.

Spears celebrated her boys’ special days – Preston turns 3 on Sept. 14, and Jayden turned 2 on Sept. 12 – with sister Jamie Lynn Spears, her newborn niece Maddie Briann, dad Jamie and mom Lynne.

Held at close friend Adrienne Maloof-Nassif’s Beverly Park house, the outdoor party drew some famous guests, including Jenny McCarthy with her son Evan, and Gwen Stefani‘s son Kingston, 2, who came to the bash from an equally starry affair: He celebrated Heidi Klum‘s son Henry’s 3rd birthday at the model’s Beverly Hills house along with all three of Victoria Beckham‘s sons.

But the guests of honor seemed to be having the best time. Preston and Jayden drove around the party in mini motorized cars, which were customized Ed Hardy by Christian Audigier. The cars featured tattoo-inspired decals, Ed Hardy air fresheners and personalized license plates. To keep with the party’s theme, the cake was in shape of a yellow truck.

“The boys received tons of birthday gifts,” a source told PEOPLE. “Britney and her family really made the party special for the boys.”