The 52-year-old actor helped his son, John, celebrate his 21st birthday in Vegas at OMNIA Nightclub inside Caesars Palace on Friday night, both looking handsome in black button down shirts and black pants. Patrick Schwarzenegger, 23, was also there for the festivities, looking sharp in a gray and white shirt. The group posed for a pic together, along with Rob's older son, Matthew.
John definitely had a lavish birthday to remember, partying with the crowd who held up giant cut-outs of his face. Resident DJ Calvin Harris performed his hits, as the group was escorted to a VIP table.
John seemed excited to be celebrating his birthday in Sin City with his family and friends, a source tells ET, as the group sipped cocktails, danced, and took photos together. However, Rob didn't partake in the cocktails -- the actor has been sober for over 25 years.
Aside from his club night, Rob's youngest son also had a more low-key birthday celebration with just his family, including his mother, Sheryl.
"#Birthday #vegas 21 and done!!" Rob instagrammed a cute snap of the family of four enjoying a chocolate birthday cake.