Nicole Richie may be a doting mom these days, but she still has a wild side.

Richie, 26, a former fixture on the L.A. late-night scene, and her beau, Good Charlotte rocker Joel Madden, 28, hit hot spot Teddy's at midnight on February 16 – just five weeks after she gave birth to daughter Harlow.

"Nicole was having a blast," a witness says in the latest issue of Us Weekly, on newsstands now. "She was her old self again – not in a bad way, but she was letting her hair down."

Another source tells Us that after the Richie and Madden found a table by Samantha Ronson's DJ booth, "Lindsay Lohan headed over and hugged Nicole" – and then the group grooved to Hanson's "MMMbop."

When Britney Spears' "Gimme More" came on, Richie even climbed atop her booth and "danced crazily," the second clubgoer told Us.

But that was as raucous as it got: Richie (who gushed to guests about being a mom) and Madden stayed just 45 minutes.