Catherine fed a lamb on her visit the site, run by Farms for City Children, which was set up to allow young people from inner cities to spend a week learning about farming, the countryside and food production in a practical, hands-on way.
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The Duchess toured the farm before joining a story-time session led by children's author Michael Morpurgo, who founded the charity with his wife Clare in 1976.
She joined the children as they completed work around the farm yard, working in the allotments and tending to pigs, sheep and chickens, before a short tea party rounds the visit off.
The organisation, which now has three working farms, welcomes around 3,200 children and 400 teachers a year.
During a visit to Cornwall in September last year, Kate is said to have confided to a young farmer that she secretly wanted to give the vocation a go.
Bea Hodge, 15, from Wadebridge, said the Duchess had told her she was teaching her children George and Charlotte about the farm at Sandringham and that "she'd secretly like to be a young farmer".