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Lopez is a newly divorced, singer and actress with twin toddlers, Max and Emme, whose busy schedule includes being a judge on TV's "American Idol" and releasing top 40 pop singles.
Banks, on the other hand, has had steady career on TV and in films such as recent blockbuster "The Hunger Games". Fourteen months ago, she and her husband Max Handelman welcomed their first child, Felix.
While Banks and Lopez did not share any scenes in the film, they came together to talk with Reuters about the fictional tale based on the bestselling pregnancy book of the same name.
It follows several different couples as they navigate the bumpy road to parenthood.
Cameron Diaz, Dennis Quaid, Chris Rock, Anna Kendrick, Chace Crawford and Matthew Morrison are among the all-star cast.
Over cappuccinos and sparkling water, Lopez and Banks traded stories about motherhood and how much they've changed since having little ones come in to their lives.
Q: Jennifer, in the film, your character Holly adopts a baby because she and her husband can't have kids. In real life, you were pregnant with twins. How did you relate to her?
Lopez: "Because of how much she wanted a baby. I had wanted a baby when I got married so badly. I already felt like I had waited too long. It took me three years to get pregnant (with ex-husband Marc Anthony) and during those three years, I was like, 'Gosh, maybe this is not going to happen. Maybe this is not meant for me. Maybe my life is about something else...' So I related to that wanting."
Q: Really? You have always projected an image of having everything - success in career, beauty and love.
Lopez: "When you've paved this path of being an actress or a singer, people see you and go, 'Oh your life is great and whole and complete - and you have money. That's all you need!' The truth is, that's all amazing but you really need that core. You need life, you need family, you need love. And even though Holly had a great life and a great relationship, there was still something missing - that want, that need to have a baby, to have a family, to have roots. I know what it feels like to want that so badly and finally get it."
Q: Elizabeth, you had baby via a surrogate. In the film, your character Wendy is pregnant, but it's not a glamorous pregnancy by any means. How did you connect with her issues?
Banks: "I was drawn to the authenticity of Wendy's experience. One of the things I liked about this movie is that it's not all happy, sugar coating. It's about the run-up to parenthood, which is scary and emotional and messy. It's a complicating factor in a relationship, no matter what. I loved that I had the opportunity, as Wendy, to say it like it is. And be messy and out of control."
Lopez: "I think everybody wants to have that perfect pregnancy where you look like Audrey Hepburn in your flats. I certainly tried. I had my leggings and my black turtleneck. Then someone took a picture of me from the back I was like, "IS THAT HOW WIDE I LOOK?!?!?!" On that same topic, I always feel like everybody loses their weight so fast, but that is not true! My ribs - I feel like they're just starting to get back to normal, yet my babies are four."
Q: As mothers working in entertainment, do you find your kids' childhoods vastly different from your own rearing?
Lopez: "The other day, my daughter put on my sparkling Louboutins that I have for shows and a Cartier ring that her dad gave me. I was like, 'What are you doing?!' (laughs) We're so fortunate that we have so much and the kids get some of that. But I don't want them to grow up that fast. I want to them to be like I was in the Bronx, wearing sneakers with holes in them!"
Banks: "I rarely buy my son anything, but he's not deprived. He gets lots of gifts. I'm like, 'We don't need all this stuff.' I'm constantly getting it out. It's too much crap."
Lopez: "I'm the opposite. I'm like, 'Oh that would be cute for a girl.' I buy everything. It's so bad. I still have their cribs in their room. They sleep in their bed but their crib is there and I'm like, 'I can't get rid of that. It's so beautiful!' Then I'm like, 'They're going to be five soon, it's going to be weird!' Even to take the bassinet out of my room --"
Banks: "I still have the bassinet. It's in my guest room, which is really weird when people come over to stay. They're like, 'Well you're clearly having another one.' I'm like, 'I don't know what's gonna happen, but I can't get rid of this beautiful bassinet!'"
Q: How has motherhood changed you?
Lopez: "There's a depth of feeling that you have not felt before. But you also feel guilt and fear deeper. I feel more scared of things now because of my kids. I feel more worried. Everything's more. I went jet skiing and flew off the jet ski. I was like, 'I'm a terrible mom! What if I were to die? What would happen to them?' It's those things."
Banks: "I've lost a full section of my brain power. It's gone. It's now devoted exclusively to him. So even though I'm talking to you, there's a part of my brain that's going, 'Did he eat today? Where is he? What's he doing?'"
Q: Switching topics real quick, Jennifer, you're in your second season on "American Idol." Has this experience been everything you hoped it would be when you first agreed to do it?
Lopez: "It was an unexpected career move. I always felt like people knew who I was but I realized they didn't. When I got on the show people were like, 'Oh, she's nurturing, she's a nice person. She's not the crazy girl (who demands) white sheets and candles.' 'Idol' let people get to know me. It gave people insight in to who I was in a positive way that I didn't expect."
Q: How has it impacted you career-wise?
Lopez: "When it was first offered it to me, I had my reservations. I love doing movies and I was like, 'Is it going to affect how people see me as a movie actress?' Even my singing. Will that part be over now that I'm a judge? But my gut was telling me - just do it. We had been travelling like crazy with Marc and his tour, so I thought, 'You don't have anything for these next six months. It's going to be fun.' It seemed like the right move at the time for my life. Then it turned out to be something fantastic."