Ashton Kutcher is "worried" about the birth of his second child.

Ashton Kutcher

Ashton Kutcher

The 38-year-old actor, who is expecting a baby with his wife Mila Kunis and already have two-year-old daughter Wyatt together, has admitted he doesn't feel as prepared for the arrival of the tiny tot like he did with his first child because he hasn't done "anything".

Speaking on 'The Tonight Show Starring Jimmy Fallon', the 'Ranch' star said: "I'm worried. The first one, I was almost like a doula. I was reading every book. I was ready. I had a catcher's mitt on. This one, I haven't done anything."

However, Ashton is consoling himself with the idea that he "didn't break the first one", so the new addition to his family shouldn't be too difficult.

He added: "I'm like, 'Well, we already didn't break the first one.' They're really durable. They don't break very easily. You have to really try to break them."

Meanwhile Ashton - who began dating the 33-year-old 'Bad Moms' star in 2012 before getting engaged two years later, and tied the knot in a secret ceremony last year - has teased the couple are expecting a boy.

Speaking on 'Today' show, he said: "She [Wyatt] points to Mila and she's like, 'Baby brother!' when she points to the belly.

"And then she points to Daddy's belly and says, 'Beer.'"

"It's intensely scary.

"How am I going to run after this one -- I thought the first one was exhausting in the beginning."

Meanwhile, Mila - who announced she was expecting another baby in July this year - has admitted she knew her and her spouse "needed" to expand their brood.

Speaking previously about her family, and plans to have more children, she said: "I've always said this, 'I think you know when your family is complete.' After we had Wyatt, the second that I gave birth, I was like, 'I know that we need to have another baby.' We both knew it, we just felt it.

"And so I always say after the second one, we'll know if we need to have another one. I really do believe you know when your family is complete."