The social media post also confirmed that Schwarzenegger gave birth to her son on Nov 8.
Meanwhile, Pratt previously opened up about his parenting style, revealing that he wants his children to “feel comfortable expressing themselves”.
The Hollywood star – who also has Jack, 12, from his relationship with Anna Faris – told E! News: “I think there’s a new age of parenting.
“I grew up, I did exactly what my parents said all the time. I never knew I could say ‘no’ to my parents. And now I’m a guy who’s not super … didn’t have a super healthy grip on his own emotions. So we’re trying to raise them in a way that they feel comfortable expressing themselves.
“They still know the meaning of the word ‘no’ from their mom. When it comes from me, they don’t seem to know what that means. And I don’t really know what to do about it, but we’ll get there.”
Pratt subsequently heaped praise on his kids, describing them all as “wonderful”.
He said: “They are cute and they’re wonderful. They’re sweet, polite, kind, joyous little angels, and I love them.”