Kate, 31, paid a visit to one of her favourite children's stores in Chelsea and handpicked a cosy jumper for her firstborn, aptly named "George" after the third-in-line to the throne.
The £34.99 navy sweater, which features a Union Jack flag emblazoned across the chest, is described as being the perfect choice for "afternoon tea with the Queen."
The Duchess of Cambridge also showed her keen sense of humour with a second purchase of a long-sleeved grey T-shirt. The £14.99 top, also from Trotters on the King's Road, is printed with three royal Buckingham palace guards, which Prince George will no doubt grow up seeing at his grandmother's majestic home.
"Kate thought they were great fun to give George," a royal insider told The Mirror. "He'll be King one day so the flag is very appropriate."
Kate and Prince William have planned to take George to the Queen's traditional gathering at Sandringham for his very first Christmas this year.
Presents are usually kept in the Red Drawing Room, with tapes showing where each person's offerings should be. It wouldn't be surprising if Prince George's pile is a little higher given the excitement generated by his arrival.
The Queen and Prince Philip are often joined by up to 30 guests at their Norfolk estate, with family arriving from 23 December. Many are youngsters and will no doubt want to play with the newest member of the royal family.
On Christmas Eve, the Queen's grandchildren and great-grandchildren are encouraged to put the finishing touches to the Christmas tree and presents are opened followed by candle-lit black tie dinner.
On Christmas Day, the British royals attend a service at the nearby St Mary Magdalene Church, followed by a full Christmas lunch. Everyone gathers around the TV in the afternoon to watch the Queen's televised speech.