Harris and son Gideon enjoy a fun day out in Brentwood, Calif. Plus: Jen & Justin, Camila McConaughey, Taylor Swift and more

PUMP IT UP

After revealing her slimmed-down bod in Shape magazine, Britney Spears trades in her bikini for an equally sexy Roberto Cavalli LBD at Saturday's 102.7 KIIS-FM's Wango Tango music fest in Carson, Calif.