The long-time pals hit up West Hollywood's Voyeur nightclub, joined by a few friends in a cozy corner booth.
The celeb moms appeared to have had a few drinks – there was a bottle of Grey Goose on their table – but kept a low profile. Richie, 28, rocked a sequined blazer and Aguilera, 29, was dressed down in jeans, a white shirt and a fedora-like hat.
Escorted through the back exit, they left the club at about 1 a.m. – just a little past their kiddies's bedtimes!
Reporting by ABBY STERN