Kensington Palace has accused paparazzi photographers of harassing Prince George and Princess Charlotte, accusing them of going to "extreme lengths" to get pictures and urged the media not to use the images.
In a letter issued on Friday, the palace said photographers were using surveillance techniques to try to get pictures of the young royals.
On one occasion last week, a photographer set up a "hide" in his car as he staked out a children's play area.
Other incidents have included:
In the letter, Kensington Palace communications secretary Jason Knauf said: "It is of course upsetting that such tactics - reminiscent as they are of past surveillance by groups intent on doing more than capturing images - are being deployed to profit from the image of a two-year-old boy.
"In a heightened security environment such tactics are a risk to all involved.
"The worry is that it will not always be possible to quickly distinguish between someone taking photos and someone intending to do more immediate harm."