The 35-year-old reality star irked his ex-girlfriend - with whom he has kids Mason, eight, Penelope, six, and Reign, three - by introducing Sofia to the children, having previously promised Kourtney that he'd wait for the right moment.
Speaking to Kris Jenner on a new episode of 'Keeping Up with the Kardashians', Scott said: ''Last night when we got home, the kids were there, so of course they met my girlfriend.
''Kourtney goes, 'You're a f***ing joke. You don't care. We discussed with the therapist that we were going to wait.' I said, 'We discussed with the therapist that we were going to wait until after the new year and after the holiday!' ''
Kris, 62, subsequently conceded that Kourtney was being slightly hypocritical about the situation, having already introduced Younes Bendjima, her then-boyfriend, to the kids.
She said: ''I don't understand why she can introduce her boyfriend to the kids but you can't introduce your girlfriend.
''She's my daughter and I don't want to go against her, but I see your point, too. So I would just ask, 'Why isn't it mutual?'''
But Kourtney - who split from Younes in August - insisted that for their children, the situation is likely to be ''confusing''.
She continued: ''It makes me upset, especially because we sat in front of a therapist, we said what we thought was best for the kids. We felt like a lot of changes have been made lately and that this wasn't the best time.''
Ultimately, Scott admitted he could have dealt with the situation better and he insisted he'd never intended to upset Kourtney.
He said: ''My biggest mistake was not being as clear as possible.
''I should have told Kourtney exactly what was happening, and I do realise this is something that can be hard for somebody. But by no means was I looking to make this any harder.''