The duchess told all to the Happy Mum Happy Baby podcast hosted by Giovanna Fletcher, who has also written about being a mother to three children with her husband Tom Fletcher, a member of the band McFly.
Asked if she struggled from "mum guilt", the duchess replied: "Yes absolutely – and anyone who doesn't as a mother is actually lying. Yes – all the time."
Kate who has a nanny, Maria Teresa Turrion Borrallo, said during the podcast: "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."
She said: "And you know, even this morning, coming to the nursery visit here, George and Charlotte were like, 'Mummy how could you possibly not be dropping us off at school this morning?'
"But no, it's a constant challenge, you hear it time and time again from mums. Even mums who aren't necessarily working, aren't pulled in the directions of having to juggle work life and family life – there's always something."
Kate added: "And always sort of questioning your own decisions, and your own judgments, and things like that, and I think that starts from the moment you have a baby."
Kate's interview was recorded at the end of January after the duchess made an early-morning visit to a nursery and pre-school in Stockwell, south London, and she joked about how her two eldest children chastised her over her priorities as a mother.
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.
Because of the illness she described herself as "not the happiest of pregnant people", adding: "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."
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."
Kate said she wanted to begin a "generational change" in early years development, and highlighted her Five Big Questions On The Under-Fives survey, launched in January to spark a UK-wide conversation about creating the best foundations for children to thrive.
The month-long online poll is thought to be the biggest survey of its kind and the data will guide the duchess' future work. It has so far attracted 200,000 responses.
Kate said: "What we're doing with the survey is asking people – what is it that matters for them in raising their children today.
"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."
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 realise the importance of "mind over the body" after trying everything to overcome the illness.
She joked: "I'm not going to say that William was standing there sort of, chanting sweet nothings at me. He definitely wasn't. 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 realised that this was something I could take control of, I suppose, during labour. It was hugely powerful."
Kate was asked what parts of her childhood she wanted to give to her children, and spoke poignantly about a picture of her 4-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."
