Later, as the Prince of Wales was shown a range of commemorative china to mark the birth, he told Trevor Johnson, of the manufacturers Caverswall: "Ah, you're doing that. Well, it won't be long now."
Kate is understood to be staying at Kensington Palace, less than 2km from St Mary's Hospital, Paddington, where she will give birth in the private Lindo Wing.
Prince William is in Wales, where his RAF Search and Rescue squadron is stationed, but has borrowed a helicopter so he can fly to London at a moment's notice.
But for other members of the royal family, it has remained business as usual.
The Queen spent the afternoon looking around the festival celebrating the 60th anniversary of her coronation.
In a departure from the usual protocol, the Queen agreed to pose with a 7-year-old girl who asked if she and her teddy could have a picture taken with her.
Jessica Fitch, of Cheltenham, Gloucestershire, approached the monarch with Bertie Bear, the mascot of the Bethesda Methodist Church Brownie pack, as her father Michael, 35, asked: "Ma'am, would you mind if we took a picture?"
The Queen, who normally declines requests for pictures, agreed, and asked Jessica: "Are you a Brownie?"
Jessica's mother Heather, 39, said: "She told her 'yes I am', and she said it in such a posh voice. It was so kind of the Queen to stop."
Jessica said: "I was a bit nervous. She was lovely."
Later, the Duchess of Cornwall said hello to the family as she passed, and she, too, agreed to a photograph.
A few minutes later, the family spotted the Prince of Wales, and completed a trio of photographs.