BRITNEY SPEARS’ sons' out of control are playing with fire as they fool around with cigarettes and lighters as they ape party-hearty parents’ smoking, boozing and cussing!

The wild antics of Sean Preston, 6, and Jayden James, 5, have outraged their dad Kevin Federline, say sources.

“Kevin puts the blame for their bad behavior squarely on Britney,” one insider told The ENQUIRER.

“She doesn’t believe in controlling the kids. Once, they got into her makeup and painted each other and the walls. Rather than discipline them, Britney just threw them out of her room and slammed the door.

“She thinks most of theirantics are just ‘boys being boys,’ and it drives Kevin up the wall. He’s convinced she’s too permissive and is ruining the kids.”

Kevin, 34, has full custody of the two little rascals, but Britney, 30, is allowed to have them three days a week and overnight every other weekend. And that’s when they seem to act up the most, according to the source.

Once, Jayden grabbed a pack of his mother’s cigarettes, and he and Sean pretended to puff away.

“Then Jayden figured out how to use the childproof lighter and actually fired up a smoke,” said the insider. “Meanwhile, Sean has been pretending to smoke since he was 2 and even tried to light a lollipop like a cigarette.

“And the kids mimic their dad’s drinking and staggering around. They’ll swig their milk or juice, slam the glasses down and ask for another ‘shot.’ Then they’ll act drunk, bumping into each other.

“They also cuss like sailors, which they must have picked up from their parents.”

Even more disturbing, the free-wheeling youngsters like to play with the candles Britney leaves burning around the house. They seem to be fascinated by fire.

“At a recent family get-together, Kevin wouldn’t let his kids light the barbecue pit, but later they were caught trying to start their own fire with one of Britney’s lighters in their room,” revealed the insider.

“Kevin’s fit to be tied. He says he’s had it with Britney’s ‘lazy mothering.’”