Britney Spears' sons shocked onlookers by swearing in public.

The 'Radar' singer took three-year-old Sean Preston and Jayden James, two, to a 'swag suite' - where invited guests are invited to select a variety of goods for free - for the Teen Choice Awards in Los Angeles last weekend when the boys repeatedly shouted "oh s**t!"

One onlooker told the New York Daily News newspaper: "We were all surprised by their potty mouths, but it was actually pretty funny."

Although their bad language attracted the attention of those around them, Britney didn't appear to notice her sons were using offensive words.

The onlooker added: "She was too busy picking out freebies to chastise the boys for misbehaving."

Britney, 27, has previously spoken about her children cursing, claiming they picked up the foul phrases from their father, her ex-husband Kevin Federline.

She said: "The boys are staring to learn words like 'stupid,' and Preston says the F-word now sometimes.

"He doesn't get it from us. He must get it from his daddy. I say it, but not around my kids."