Nicole Richie, Christina Aguilera Have Moms' Night Out!

Credit: JCalderon/Splash News Online

Mommies' Night!

Nicole Richie and Christina Aguilera left their kids and men at home Thursday night -- hitting L.A. hotspot Voyeur for some girls-only fun.

Both wearing cleavage-bearing tops, Richie and Aguilera rolled into the club around midnight with some friends and bodyguards. The two stars settled into a corner VIP table and sipped champagne. "They chatted the whole time," a Voyeur witness says. "They were sitting on top of the banquette, listening to the music and chatting."

The pair have a lot in common. Designer Richie, 28, has two kids with rocker fiance Joel Madden: daughter Harlow, 2, and son Sparrow, 10 months. (The longtime couple announced their engagement this February, although they haven't yet announced a wedding date.) Singer Aguilera, 29, wed music executive Jordan Bratman back in November 2005 -- and their son Max is one day older than Harlow.

"They looked like they were having fun," the Voyeur witness adds. At one point, the friends high-fived one another and were "laughing hysterically."