03/05/2007 at 05:20 PM EST
While Britney Spears remained in rehab, Kevin Federline headed to Las Vegas over the weekend – with the kids.
Federline was in town for a long-planned paid appearance at the Mirage Hotel & Casino lounge Revolution, sources tell PEOPLE.
"Kevin was really low-key," one source says. "You could definitely tell he was on his best behavior. He was having a good time, but wasn't the wild, crazy Kevin who used to come to Vegas."
Federline also plans to return to Las Vegas on March 24 to celebrate his 29th birthday at Pure Nightclub, PEOPLE has learned.
In his latest trip, he arrived on Saturday with Sean Preston, 18 months, and Jayden James, 6 months, plus a nanny, his mother and brother and two bodyguards, sources say.
He had dinner with friends and family at the hotel's Japonais restaurant, says a source, who adds: "He was late for dinner because he wanted to tuck his kids into bed."
By midnight, he was relaxing at a VIP table at the Revolution with a group of friends who included Las Vegas comedian Jeff Beacher.
Spears's rehab ordeal, says a source, has matured Federline.
"He wakes up with a purpose each morning and has enjoyed his family being around him," says the source.
A rep for Federline declined to comment.