Gwen Stefani was in a bikini yesterday for an afternoon out in Malibu with her husband Gavin Rossdale and their sons Kingston and Zuma. She looked super fit in her black top and long skirt combo, which showed off her amazing abs. Gavin, meanwhile, was shirtless to wade into the Pacific with Zuma and Kingston. It was the end of a fun week for the foursome, which kicked off on the previous Saturday when Gavin's band Bush performed at the Sunset Strip music festival. Gwen's group No Doubt has been able to enjoy a brief hiatus from finishing up their new music, since Tony Kanal is off on a vacation celebrating his birthday. Gwen and Gavin also made sure to pack the last few days with good times in honor of Zuma turning 3. His big day was on Aug. 20, and he was able to wear costumes, get a manicure, and bond with his brother to mark the milestone.