This sweet little brooch was given to Queen Elizabeth in 1948 by her father George VI when she gave birth to Prince Charles.
She wore it in her official portrait with the new baby:
The Queen then wore it to her great-grandson Prince George's christening, to make the link between King George VI and the future King George VII - as you can see in this historic picture of the Queen and the three future kings:
Though the brooch looks light and pretty it's actually very expensive as it is made of diamonds, rubies, sapphires and emeralds.