The Duchess of Cambridge, who is seven-month pregnant and due to give birth in July, has decided to hold the celebration despite the fact that the event is not included in Britain's royal tradition.
31-year-old Kate, married to second-in-line to British thrown Prince William, has the blessing of Queen Elizabeth II for the event with family and friends after weeks of planning by her 29-year-old sister.
The celebrations will be a real family affair, including a cake in the shape of a dummy made by brother James, who runs his own baking firm.
The source said: "She is modern and wants a normal life. Prince Harry, Kate and William are the Royal Family's link to the younger generation."
"A baby shower wouldn't normally happen if you're in the Royal Family, but there is now a modern way of thinking. It will be a great day for everyone and Kate is doing this with the blessing of the Queen."