The Queen Consort declared that the Christmas season has officially begun as she enjoyed a visit from Santa and his reindeer to Clarence House.

Father Christmas was joined by some special little helpers to decorate a Christmas tree in the library at the royal residence.

Young people from two charities which care for seriously ill children hung festive trinkets on the tree, with Camilla’s equerry Captain Ed Andersen at one point using his sword to place them high up on a branch.

Participants at Wednesday’s event included families supported by Helen and Douglas House, which cares for terminally ill children and their loved ones from Oxfordshire and the surrounding counties, and those supported by Roald Dahl’s Marvellous Children’s Charity which provides specialist nurses and support to seriously ill children with some of the most complex health conditions in the UK.

As Camilla, wearing a festive red wool crepe dress by Fiona Clare, met the charity’s bosses and Santa, the Band of the Welsh Guards performed Once In Royal David’s City.

Camilla, patron of both organisations and hosting the annual event for the first time since become Queen Consort, thanked the charities’ staff for the work they do and the respite they give parents.

She said: “It’s always a treat for me to start the Christmas season here, it literally kicks it off for us. And I’d really like to say a huge thank you to all of you because I’m sure all the parents here are so indebted to what both the charities do for your lovely children.

“So I’d just like to wish you all a very, very happy Christmas.”

At one point Camilla helped to hand out plates of specially made dishes including sausage and mash in the dining room to suit each child’s dietary requirements.

Roald Dahl’s widow Felicity Dahl, founder of the Marvellous Children’s Charity, praised her for her continued support, describing the event as “charming”.

She said: “She’s the most amazing woman. I think she’s unbelievable and, you know, talks to everyone. (It’s) exhausting but she does it and she does it with such grace.”

Mrs Dahl said she wished her late husband could have been there.

“His passion was medicine, if he hadn’t been a writer he’d have been a doctor,” she said.

The children got a special surprise when they went outside to be greeted by two reindeer – Dancer and Blitzen.

Camilla joined the young people as some of them fed the animals lichen – known as reindeer moss.

Camilla told Gwendolyn Dainty from Oxfordshire that her tiara was “very pretty”.

The girl’s mother Kieri said her daughter had insisted on wearing it to meet a real queen.

Mrs Dainty described the event as “really special”.

She said: “It’s lovely because I think for a lot of parents of children with needs it can be quite lonely, so to do something like this is really special.”

She praised Helen and Douglas House for being “incredible” with her daughter, who lives with a number of conditions including cerebral palsy and epilepsy.

Its chief executive, Clare Periton, said the event is “absolutely magical” for the children and that there is “extra excitement” this year.

She said: “For our families and the other charity’s families to come within the first few months of her being Queen, it just shows how she values her patronage to us and she cares about the children and the families that use the services.”

Louise Griew, chief executive of the Marvellous Children’s Charity, said the event allows families “a chance to make really special memories”.

She described Camilla as “warm” and “funny” in her role as patron, saying she is “instrumental” in raising people’s awareness of the charity.

She said: “We’ve got really good plans over the next five to 10 years to help thousands more children so having her involved in the charity is instrumental and it really does help us.”

In her former role as the Duchess of Cornwall, Camilla became patron of Helen and Douglas House in 2007, while she became patron of Roald Dahl’s Marvellous Children’s Charity in 2017.