The duchess joined the pupils during a visit to Lavender Primary School in Enfield, north London, to mark Children’s Mental Health Week.
The youngsters had been asked to share objects that represented something that made them feel good.
When Kate first arrived children had gathered outside the school building and sang songs to welcome her.
Later the duchess, who wore a dress by Eponine, will go to north-west London to learn how the school of award-winning Andria Zafirakou, named the world’s best teacher, is supporting the wellbeing of pupils and staff.
Ms Zafirakou was awarded a million dollars (£766,000) in prize money and the 2018 Varkey Foundation Global Teacher Prize, which recognises an individual who has made an outstanding contribution to the profession.