Paris: I Want Kids – 'Soon!'

By Mark Gray

10/06/2008 at 08:10 AM EDT

Even while sipping Grey Goose out at a club, Paris Hilton has babies on the brain.

"I definitely want three or four [children]," she told PEOPLE in Las Vegas Saturday night, while partying at Pure Nightclub for her sister's birthday.

As for a timeline? "Soon," she said. "Maybe a year or two."

In the meantime, she's just enjoying domestic life with beau Benji Madden. "We just had our 7 month anniversary," she gushed. "We are just so happy."

Add sister Nicky – who just turned 25 – to the "so happy" list.

The entrepreneur said she's "content" with longtime boyfriend David Katzenberg. Still, "there are no wedding plans," she added. "There are lots and lots of rumors but I will put them to rest."

As the party raged on until 3 a.m., Paris jumped on the microphone to give a shout-out to "the best sister in the world." Moments later, the Las Vegas Pussycat Dolls presented Nicky with a three-tiered cake as the entire club joined them in singing "Happy Birthday."

"Twenty five is a pretty milestone year," Nicky told PEOPLE at the bash. "I'm officially an adult!"