Kate confessed to struggling with "mummy guilt" and said she tried "hypnobirthing" when pregnant during the "Happy Mum, Happy Baby" podcast.
In the candid discussion about parenthood, on the podcast released Saturday, Kate responded, "Yes absolutely, and anyone who doesn't as a mother is actually lying. Yes, all the time," when asked if she ever experienced "mum guilt."
Kate -- the mom of Prince George, 6, Princess Charlotte, 4, and Prince Louis, 1 -- described herself as a "hands-on mum", but said she often feels she falls short of expectations about being a mother.
"There's such a pull, but I am such a hands-on mum, and whatever you're doing you want to make sure you're doing the uttermost best job you can for your children," said the duchess, who has a nanny, Maria Teresa Turrion Borrallo,
She also admitted to not being the "happiest" of people while pregnant.
"Lots of people have it far, far worse, but it was definitely a challenge. Not just for me but also for your loved ones around you," she said about her difficult pregnancies.
At the start of all of her pregnancies the duchess suffered from a form of morning sickness called hyperemesis gravidarum, which causes severe vomiting and can lead to dehydration, weight loss and a build-up of toxins in the blood or urine.
The duchess went on to say: "You know, William didn't feel he could do much to help and it's hard for everyone to see you suffering without actually being able to do anything about it."
The duke revealed in 2017 when his wife was pregnant with Prince Louis that they had been trying a host of remedies after a well-wisher said Kate should nibble on ginger biscuits.
He replied at the time: "Ginger biscuits -- but there's not much ginger can do to stop that, we've done all that."
The duchess explained how her experience with the severe morning sickness led her to hypnobirthing, as she came to realize the importance of "mind over the body" after trying everything to overcome the illness.
"I'm not going to say that William was standing there sort of, chanting sweet nothings at me. He definitely wasn't," she joked. "I didn't even ask him about it, but it was just something I wanted to do for myself."
"I saw the power of it really, the meditation and the deep breathing and things like that, that they teach you in hypnobirthing, when I was really sick, and actually I realized that this was something I could take control of, I suppose, during labor. It was hugely powerful."
She also spoke about the keys to a good childhood based on her own upbringing.
"One is quality of relationships, so those moments that you spend with people that are around you," Kate told podcast host Giovanna Fletcher. "I remember that from my own childhood."
"I had an amazing granny who devoted a lot of time to us, playing with us, doing arts and crafts and going to the greenhouse to do gardening, and cooking with us," said Kate, who has two younger siblings. "And I try and incorporate a lot of the experiences that she gave us at the time into the experiences that I give my children now."
Kate -- who brought William, George and Charlotte to the "Back to Nature" garden she designed last year -- also spoke about the importance she places on spending time outdoors with her kids.
"There are also the environments you spend time in as well: a happy home, a safe environment," she said. "As children, we spent a lot of time outside and it’s something I’m really passionate about."
I think it’s so great for physical and mental well-being and laying [developmental] foundations," Kate said of the outdoors. "It’s such a great environment to spend time in, building those quality relationships without the distractions of ‘I’ve got to cook’ and ‘I’ve got to do this,' and actually, it’s so simple.”
When asked what parts of her childhood she wanted to give to her children, and spoke poignantly about a picture of her four-year-old daughter, she said, "I've got this one photo of Charlotte smelling a bluebell, and really for me, it's moments like that mean so much to me as a parent."
"And I try every day to put moments like that in, even if they're small or even if I don't have time - but that in an ideal world (that) is what I would like to do," she added.
Fletcher told "Good Morning America" that she never expected Kate to be so candid in her first-ever podcast interview.
"I've never heard her speak in that way before," Fletcher said in an interview that aired Tuesday on "GMA." "You hear her be self-deprecating, that laughter the way that she talks about her husband, her children, her childhood, there is that playfulness in her voice."
Fletcher said she found Kate's description of Charlotte smelling a bluebell flower particularly relatable for other parents like herself.
"So many parents can relate to those moments," she said. "The best times, the ones that really sit with you, are the ones that just happen spontaneously on their own."
The survey includes questions on topics like what's most important for kids to live a happy adult life, who holds responsibility for giving kids the best shot in life and which period of a child's life is most important for health and happiness as adults.
"I want to hear the key issues affecting our families and communities so I can focus my work on where it is needed most," Kate said in a statement announcing the survey's release in January. "My ambition is to provide a lasting change for generations to come."
Kate has made early childhood development a focus of her royal work since becoming a mom herself.
The Duchess of Cambridge is known for incorporating hands-on visits with kids, parents and caregivers into her royal engagements.
Since announcing the "5 Big Questions on the Under Fives" survey, Kate has toured the U.K. to meet with kids and caregivers and encourage people to participate.
"It’s going to take a long time – I’m talking about a generational change – but hopefully this is the first small step: to start a conversation around the importance of Early Childhood development," Kate said about the survey's aim. "It’s not just about happy, healthy children. This is for lifelong consequences and outcomes.”
ABC News' Tony Jones, contributed to this report.