Kate has launched a Blue Peter competition and called on viewers of the programme to come up with an idea for an interactive piece based on nature.
The winning entrant will have their sculpture built and installed in the duchess’s garden, which was showcased at the Chelsea Flower Show, when it moves to RHS Wisley, Surrey in September.
Blue Peter Badge-holder Kate appears in a special film, which will be shown on Thurday’s edition of the BBC show. She will be given a green Blue Peter Badge for her efforts.
She talks about her love of the outdoors and how her children Prince George, Princess Charlotte and Prince Louis are "dragged outside", whatever the weather.
Kate is shown taking part in pond dipping, planting and team den building with Blue Peter presenter Lindsey Russell and local school children at Westminster City Council's Paddington Recreation Ground.
She tells Russell how she enjoys spending time with her family outdoors, laughing saying: "Rain or shine, they're dragged outside. It's great. It encourages creativity, confidence and even a short amount of time - 10 or 15 minutes outside - makes a huge difference to both physical well-being but also to our mental well-being."
The duchess, with her sleeves rolled up and gardening gloves on, plants flowers in a metal watering can, as the school children use old wellies as up-cycled plant pots.
She tells how, while looking for newts and tadpoles, pond dipping is "massively up my street, yes definitely. I love it". Chatting to the children, Kate says: "What things have you guys found when you've been here? ...Do you know what the tadpoles eventually turn into? Have you ever seen any froggies?"
As one girl picks up a newt, Kate says: "Look at you. Well done. That is amazing."
Kate and Russell are also challenged to a team building competition by young gardener and RHS ambassador George Hassall, who splits the group into Team Catherine and Team Lindsey.
"There's so many cool things in here," Kate says as they as they search for logs for their structure.
"I love it, but I am in your hands," the duchess says of den building.
Crouched inside her finished den, the duchess asks the children: "Shall we make a name for our den? What do you think we should we call it?."
To the idea Den Of The Day, she replies: "Den of the Day - I like that. Well done. You did an amazing job and you did it seriously quickly."
When the winner is announced as Team Catherine, Kate gives a "woo", a double thumbs up and claps.
The duchess, dressed casually in her buttoned-up Troy Tracker jacket, black skinny trousers and sage-coloured pumps, was wearing her gold Blue Peter badge.Kate and William play with young royals at Chelsea Flower Show
A delighted Kate was presented with a new green "environment, conservation and nature" Blue Peter Badge.
Kate gained her rare gold badge after appearing on the show with husband the Duke of Cambridge in 2017, receiving the honour for their work on children's mental health.
The Royal Garden competition, which runs from June 13 to June 25, is part of the duchess' mission to encourage children and families to get back to nature, and highlight the positive impact that nature and the environment can have on childhood development
Her woodland wilderness garden at the Chelsea Flower Show in May featured a high-platform tree house, a rope swing, a rustic den and a campfire as well as tree stumps, stepping stones and a hollow log for children to play on.
George, Charlotte and Louis were taken on a visit to see it by Kate and William, and the Cambridge children spent around an hour playing in its stream and running around its woodland paths.
The Blue Peter episode featuring the duchess will be shown on Thursday June 13 on CBBC at 5.30pm.