Sometimes, a working mother just needs to blow off a little steam. Which is why we can hardly blame Nicole Richie – mom to daughter Harlow, 5 and son Sparrow, 4 – for leaving the kiddies with dad Joel Madden while she enjoyed a little grown-up time with friends at the Art Basel festival in Miami on Dec. 5.

That evening, Nicole arrived at local hotspot Rec Room in the Gale Hotel with three pals in tow. Looking stylish as ever in black fur with her hair slicked back, Nicole and her posse took a table in the back and ordered up a round of drinks.

“They were drinking tequila,” a fellow partier tells Wetpaint Entertainment. “They didn’t really mingle with other guests, they were just having fun hanging out by themselves.”

Nicole and the gang were so immersed in their conversation, we’re told they didn’t even notice  Adrien Grenier singing karaoke at the other end of the bar!

“He was goofing around onstage,” the partier notes. “It was really funny.”

Nicole and Adrien aren’t the only celebs partying it up in Miami for Art Basel. Kim Kardashian, Kanye West, Lindsay Lohan, Leonardo DiCaprio and Nicole’s dad Lionel Richie have also been spotted soaking up the rays – and the art – this week.

Meanwhile, Joel's having some fun at his wife's expense while she's out of town. "Nicole is away for the weekend, so I'm giving away all of her sweatpants," he tweeted yesterday. "Tweet me if you want some..."

Hey Joel, got any left?