They're budding socialites!

Kendall and Kylie Jenner, a.k.a. the youngest of the Kardashian bunch, hit the streets once again on Saturday night to support their brother Brandon Jenner and his performance at the Troubadour in West Hollywood.

The sisters have been under some flack for partying at a 21-and-up night club in L.A. with Scott Disick and Khloe Kardashian earlier this week. The California Department of Alcoholic Beverage Control is even investigating the situation.

Last night, the sister duo attended with Nicole Richie's half-sister Sofia, 15, and dad Bruce, 63. Looks like he was the only legal one of the bunch ...