Camilla spoke to the children and their families, who have all received support from the children’s hospice Helen & Douglas House and Roald Dahl’s Marvellous Children’s Charity.
She helped to serve the children’s lunch before the surprise visit of Dancer and Blitzen, the “Randwick Reindeer”, to the Clarence House garden.
The duchess also helped the children decorate the Clarence House Christmas tree.
Clare Periton, chief executive of Helen & Douglas House, said: “The biggest thing we do is the symptom control, enabling children to enjoy life as much as they can.”
Roald Dahl’s Marvellous Children’s Charity supports a network of more than 70 specialist nurses across the country.
Each year, the nurses help an estimated 21,000 children suffering from chronic and often underfunded conditions such as epilepsy, sickle cell anaemia and “Syndromes Without A Name”, otherwise known as Swan, the charity said.
This year marks the ninth time that families and hospice staff associated with the charity have been invited to decorate the Clarence House Christmas tree, and the third time for those from Roald Dahl’s Marvellous Children’s Charity.