Mothers everywhere feel guilt and self-doubt about their parenting abilities, and those who happen to be movie stars are no exception.

This is why Mila Kunis, 34, and Kristen Bell, 37, instantly related to the premise of their new comedy, A Bad Moms Christmas, which opens in Singapore tomorrow.

Speaking to The Straits Times at a press event in Los Angeles last week, Kunis admits she often feels guilty about not spending enough time with the three-year-old daughter and one-year-old son she has with actor husband Ashton Kutcher.

"Yes, I sometimes feel like I'm a failure as a mom. Of course. Today, I won't see my kids for 10 hours - do you think that makes me feel good? Nope," says Kunis, who had starred in Black Swan (2010) and Friends With Benefits (2011).

The actress also feels a pang when she returns home and her children do not seem to have missed her all that much. This happened after a recent work trip to Chicago.

While she was away from her home in Los Angeles, her daughter Wyatt rang her. "She was saying, 'I miss you so much, Mom'. And I was crying, 'I miss you too.' But I come home and she's covered in ice cream and sprinkles and is having the best time ever," she says.

Minimising time away from her family is why Kunis set up a Los Angeles-based television production company three years ago with two friends who are also mums. This allows her the flexibility of travelling to be with Kutcher when he goes on location elsewhere and still take her daughter to school regularly.

"My husband and I love what we do. We're a little bit workaholic, but we try to find the balance and I think that's okay.

"For a long time, I felt so much guilt about working because I was, like, 'I shouldn't love working so much. But I'm teaching my kid a good work ethic - she visits me at work and sees that I work hard."

Bell, too, says she is constantly reminded of her failings as a parent.

"There have been moments when I've dropped my kids off at school wearing two different shoes - one white and one black - because I got ready too fast, not wearing a bra, because that was the morning I was having," says the actress, who has two daughters, aged four and two, with husband Dax Shepard, the 42-year-old star of Parenthood (2010 to 2015).

But she "chooses to find comedy in that and not shame myself".

"Guilt is not for me. I have it, but I don't get along with it. I think it's wasted energy."

Bell, who is also the voice of Princess Anna in the animated hit Frozen (2013), and Kunis say this is the message of the Bad Moms movies, which revolve around a group of mothers who are constantly made to feel like they do not measure up as parents.

Released in July last year, the first film was a surprise hit that made US$183 million (S$249 million) worldwide, prompting the studio to quickly churn out a sequel just 15 months later.

Its stars, along with writer-directors Jon Lucas and Scott Moore, believe the original movie did well because it spoke to an under-served audience.

Says Bell: "This story was just screaming to be told for a very long time. It's an incredibly relatable thing to feel like an overworked mom. And even if you're not one, you probably had an overworked mom.

"And to discuss the idea that moms are allowed to be more than one thing feels taboo and crazy and provocative and funny."

Lucas reveals that although the first film, Bad Moms, was initially "passed over by every big studio", it clearly "hit a nerve" with female filmgoers, many of whom made a night out of going to watch it, flocking to cinemas in big groups.

The film's title is tongue-in-cheek - the women played by Kunis, Bell and Kathryn Hahn are not actually bad parents, but they slowly embrace the idea that they do not have to be perfect all the time and can simply be themselves.

And whereas the original movie dealt with the pressure put on them by other mothers, the sequel deals with another major source of stress - a big holiday such as Christmas.

In the movie, it is exacerbated by the arrival of the protagonists' own mothers, played by Susan Sarandon, Christine Baranski and Cheryl Hines.

In many countries, Christmas "is like the World Cup for moms", Lucas explains. "It is a really stressful time and most people love their families, but it's the confluence of everyone coming together and having expectations.

"There's a lot of pressure to perform for moms - it's this big show you put on. And any time we see that pressure, that's a good place to find comedy."

For Bell, being a mother itself is inherently comedic. "Because everything about being a mom is stupid and funny, you know? You always smell like urine, and there's a ton of comedy in imperfection. That's what being a mom is - dealing with your imperfection."

• A Bad Moms Christmas opens in Singapore tomorrow.