Kevin Federline was celebrating his 29th birthday over the weekend. His actual birthday is March 21. He was in Las Vegas with his kids and Shar Jackson, his ex-girlfriend. Britney Spears is in Las Angeles trying to get back into the hang of things since getting out of rehab.

Federline arrived in Las Vegas Friday afternoon with sons Sean Preston, 1, and Jayden James, 6 months. After checking into Caesars Palace, Federline spent the remainder of the afternoon relaxing in a VIP cabana at Caesars' Venus Pool Club, a private, somewhat hidden topless pool adjacent to the general-public pool, a source tells People. Festivites for his birthday started Saturday night. He started at Social House, dining on Asian fare with 14 of his closest friends and family. "He was talking on the phone and texting the whole time," said the source.

Later, Federline made his way to Caesars' Pure Nightclub, where his ex Shar Jackson was already present. "As soon as his parents got to the club they immediately went to Shar's table on the other side of the club and hung out there for a while," a source says. "They were taking photos with her and catching up. It's pretty easy to see that they still care about her."

Just before 4 a.m., Federline went back to his room, the 4,000-sq.-ft "Rain Man Suite" – where the movie of the same name was filmed.