"I've never felt more inept in my life. My 3-year-old's already running our house," Timberlake, 36, shared. “My wife and I, when we have a night off and we get him to bed and we sit down and watch a movie or something, we’re like, ‘What did we do before this? Did we go out to dinner? Were we at a bar? What did we do before this?’”
2. Ryan Reynolds
The Deadpool 2 star -- who has 3-year-old James and 1-year-old Inez with wife Blake Lively -- joked that any perceived cool status went out the window after having his first kid.
"I’ve definitely lost all cool. I'm the dad guy now," Reynolds, 41, joked with Jimmy Fallon back in 2015, also elaborating on his daughter's first words. "She’s saying ‘Mama.' What my wife doesn’t realize is [James] calls me ‘Mama,’ too. Seriously. I literally had to sit her down and tell her that penises don’t work that way. She understands -- she gets it."
3. Kevin Hart
The Jumanji: Welcome to the Jungle star recently shared with ET his delight in finding out his infant Kenzo was going to be a boy.
"It's a boy. It's a big deal, 'cause the Hart name lives on," Hart, 38, said. "Because at the end of the day, you don't want this greatness to stop. By greatness, I'm referring to myself. You want this greatness to live on."
"They vomit a lot. For a second I thought I needed to rename my first Linda Blair and hire a priest, because she was spitting up so much," Fallon, 43, shared, referencing his eldest daughter, Winnie.
The Tonight Show host also noted that all things poop has become a consistent topic of conversation.
"People think they can talk to you about poop," he said. "'Oh, you have a new baby? Is she sleeping? Is she pooping?' Normally I'd be blushing, but as a parent you just get used to it, and pooping is just another verb in your vocabulary."
"I suppose [the most real moment is] just the minute they came out," he shared a few months after the twins' birth. "None of it is real until all of a sudden they're standing there covered in slime and crying. You're like, wait a minute, what is that? We were just two and now we're four."
6. Tyler Perry
Back in September, the film director dished to ET that his 3-year-old son, Aman, is already one savvy little cookie.
"I don't do characters with the books, but he's into Paw Patrol right now, so every night he gets three books [because] I tell him, 'I'm only reading three tonight,'” Perry, 48, said. “And what he'll do is bring 10, but we only get three, so we'll read the three and then I say, ‘OK, you have to go to bed now.’ And he'll say, ‘Read them again. You said three, so just keep reading these three.’ Pretty smart already!”
"You know, it’s incredible. When you first get them, you're all excited, and you're, like, ready to do all these things," Kutcher shared of being a new dad. "And then you realize it's like getting a new cell phone where all the features don't work yet... but it looks really cute."
8. John Legend
Back in 2016, the "All of Me" singer joked to ET that his daughter, Luna, who was five months old at the time, wasn't even remotely fazed by meeting music icon Stevie Wonder.
“She has no idea,” Legend shared, referencing himself and his famous wife, Chrissy Teigen. “She doesn't know that we are famous, she doesn't know Stevie Wonder is famous. [It’s like] ‘Who are you?’”
9. Seth Meyers
The Late Night host and Saturday Night Live alum elaborated on some of the more "embarrassing" feelings that come with fatherhood.
"It is so embarrassing how I went from a person who did not care about anyone's children," Meyers told Fallon on The Tonight Show. "Then you have them, and you brag about the same stuff that you never cared about. And you tell people, he's got four teeth, like they care."
10. Kevin Costner
If it were up to the 63-year-old Yellowstone star, who has seven children, his kids' school lunches would most likely contain large amounts of sweets and barbecue.
"[My wife Christine Baumgartner and I] both drive them to school in the morning when I'm here," Costner told ET back in 2015. "Chris is great about what to eat, because if it was up to me, they'd have chocolate. You know? They'd have what's simple. 'Put some ribs in there.'"
See below for more celebrity dads talking all things fatherhood.