The BBC 500 Words competition, which received more than 46,000 entries this year, encourages children of all abilities from across the UK to write.
Camilla presented the medals and the winners will be announced during a special episode of the BBC's The One Show on March 6.
After the ceremony at Windsor Castle, the Queen met the marmalade-loving bear who has been brought to life for Paddington The Musical on the West End.
She shook hands with the 4ft creature, who was dressed in his signature blue duffle coat and red hat, and thanked him for coming to the event.
"Hello Paddington - how very nice to meet you, thank you very much for coming," Camilla told the bear.
"You're very kind, you are going to give all your marmalade sandwiches to all these children.
"Perhaps I can have one too?"
The bear gave the Queen an enthusiastic thumbs up to this request, and later guests were offered the sandwiches on plates beneath red hats.
The late Queen Elizabeth II famously appeared in a comedy sketch with a digitally animated Paddington Bear to mark her Platinum Jubilee, in which she revealed that she kept marmalade sandwiches - Paddington's favourite treat - in her handbag.
When she died in 2022, mourners left Paddington cuddly toys and marmalade sandwiches outside Buckingham Palace in tribute.
Paddington Bear wowed the audience at the final ceremony when he took to the stage to sing The Explorer And The Bear from the musical.
Since the competition was launched in 2011, by Chris Evans on the BBC Radio 2 Breakfast Show, it has received more than one million stories from children throughout the UK.
The ceremony celebrated the achievements of six winners from two age categories, five to seven and eight to 11, with recognition given to gold, silver, and bronze recipients in each group.
Sir Lenny Henry - one of the judges - told reporters he had been talking to the children who had made it to the final of the competition.
"They've all said 'I'm writing a sequel, I've got a follow-up, it's going to be amazing'," Sir Lenny said.
He joked: "Some of them have agents, there's a limo outside for one of them already, I mean they're really ahead of the game these kids, they're amazing."
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