The letter came after one photographer was found hiding in the boot of a car in an attempt to get pictures of Prince George.
The letter, penned by the royal couple's communications secretary Jason Knauf, states there have been an "increasing number of incidents of paparazzi harassment. And the tactics being used are increasingly dangerous".
One photographer discovered by police had rented a tinted-window car and created a "hide" by hanging sheets inside. Stocked with food and drinks, he then parked it in a discreet place by a children's play area, where he remained for several hours hoping to snap images of the Prince.
Other intrusive paparazzi tactics have included using long range lenses to capture images of The Duchess playing with Prince George in a number of private parks; and even using other children to draw Prince George into view around playgrounds.
Snappers have also been found hiding on private property in fields and woodland locations around Kate and Wills' home in Norfolk, and one obscured themselves in sand dunes on a rural beach to take photos of Prince George playing with his grandmother.
The letter explained that Will and Kate want their children to have freedom to play outside, saying: "The Duke and Duchess are of course very fortunate to have private homes where photographers cannot capture images of their children. But they feel strongly that both Prince George and Princess Charlotte should not grow up exclusively behind palace gates and in walled gardens. They want both children to be free to play in public and semi-public spaces with other children without being photographed."
The letter did also praise the British media for respecting the family's privacy, and that further photo opportunities to picture the heir and his little sister would take place in future. Great news because we're still loving those christening snaps from Princess Charlotte's big day.
However, the letter added that there was still a large international market for photos of the royal tots, and that two-year-old Prince George was their "number one target".
For exclusive competitions and amazing prizes visit Reveal's Facebook page NOW!