With Britney Spears remaining 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, according to snitches.

“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, 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.

“He wakes up with a purpose each morning and has enjoyed his family being around him,” says the source.