Kevin Federline in Las Vegas last weekend with the kids. He had to be there for a long-planned paid appearance at the Mirage Hotel & Casino lounge Revolution.

Source said "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." He arrived on Saturday with Sean Preston, 18 months, and Jayden James, 6 months, plus a nanny, Federline's 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' rehab ordeal, says a source, has matured Federline. "He wakes up with a purpose each morning and has enjoyed his family being around him".