The couple's representative confirmed their baby news to PEOPLE on 15 June.
Both Kunis and Kutcher have previously opened up about how parenthood has changed their lives.
"You think you know how much you can love another person, and then you have a child and you realise you didn't know. It's infinitely rewarding," Kutcher said on the Ellen DeGeneres show shortly after the birth of Wyatt.
"I think I really look at this as the greatest opportunity of my life."
Since becoming a mum, Kunis has shared her desire to have more in the future.
In October 2015 when asked about whether she'd expand her brood, she told Entertainment Tonight: "I mean, not today. I'm not pregnant.
"Not today, but yeah, absolutely. For sure!"
Congrats to the couple!