The special coins, which have been produced by the Royal Mint in Llantrisant, South Wales, have gone on sale to mark the christening of the couple's son, Prince George.
The design features the Lily Font from the Tower of London and two harp-playing cherubs.
At the foot of the coin is the royal motto "Dieu et mon droit" - God and my right.
The £5 coin is available in silver - as the crossing of a baby's palm with silver is said to confer good health and prosperity to newborns, as well as gold to commemorate the royal celebration.
William and Kate's son will be christened at the Chapel Royal, St James's Palace on October 23.
Dr Kevin Clancy, director of the Royal Mint Museum, said: "I think the designer, John Bergdahl, has done an excellent job of giving us something that is timeless."
Mr Bergdahl said: "The design is baroque, a style that has been reborn many times and often featured in royal artwork and traditions.
"One element that I knew I wanted to incorporate was the Lily Font from the Tower of London, which is a strong tradition in christenings for the Royal Family. The motto is traditional and sums up the expectation carried by a young child, born to reign - regardless of gender - for the first time ever."
Mr Bergdahl said it normally takes up to two years to produce a new coin, but the christening edition had to be made in around seven months because of the unknown details about the royal baby, such as its gender or name.