'Aww Scott and His Kids': Kendall Jenner Shades Disick and Girlfriend Sofia Richie on Instagram

Kendall Jenner isn’t holding her tongue when it comes to Scott Disick’s relationship with Sofia Richie.

On Saturday the 21-year-old model left a comment on a photo shared by a fan account of Disick, 34, riding in a car with Richie, 19, and the children he shares with ex-girlfriend Kourtney Kardashian — sons Reign Aston, 3, and Mason Dash, 8, and daughter Penelope Scotland, 5½.

“Awww Scott and his kids,” Jenner — Kardashian’s sister — wrote, adding a laughing face emoji.

A source tells PEOPLE that Disick and Richie had dinner with his kids at Nobu.

“You could tell that the kids don’t know Sofia well because they weren’t holding her hand. Instead, they all stayed close to Scott,” the insider adds. “It was a short dinner. Scott and Sofia were not affectionate. The kids seemed fine with her, but all sat close to Scott. He helped them at dinner and with potty breaks.”

Notes the source, “Sofia acted like Scott’s friend and you could tell she was trying a gentle approach to get his kids’ approval.”

While this appeared to be the first time a member of the KarJenner family had explicitly commented on Disick’s relationship with the teenager, Kim Kardashian West previously called the father of three “desperate” and “malicious” for “going out on the town” with Bella Thorne, then also a teen, in 2016.

Disick’s ex Kardashian has also since moved on. In a recent episode of Keeping Up With the Kardashians, Kardashian told her sister Khloé Kardashian that she had received a late-night phone call from Disick where he had ranted about her 24-year-old boyfriend Younes Bendjima.

“Last night, Scott called me at like two in the morning — he never calls me late at night, ever,” she said. “And he was just ranting — like, ‘What are we doing in life? What are you doing? What am I doing?’ And I’ll go: ‘But what are you doing?’ But then he’ll say: ‘But what are you doing? Is it any better?’ ”

Eventually, Kardashian had enough.

“By the end of the conversation, I just was like: ‘I have a boyfriend. He’s 24 years old. It’s not the craziest thing that’s ever happened in the world!’ ” she said. “And he was like: ‘He’s your boyfriend?!’ And then he hung up the phone.”

“It’s definitely serious,” a source told PEOPLE in December of Kardashian and Bendjima, who were first introduced during a trip to Paris in October 2016. “No one thought their relationship would last this long, but Kourtney is very happy.”

A source told PEOPLE in November that Disick and Richie — who have been datingsince September — are also “very serious” and that the daughter of Lionel Richie has been a positive influence on Disick, who has openly struggled with alcohol abuse.

“She’s been great for him,” the source said. “She’s made a big impact on his life and hasn’t partied at all since they met.”