When Petrorhagia nanteuilli is young, it looks as if it has only one flower in the head. As the flower head ages and the initial flowers in the head fade, the brown bracts open up while the head is still producing ne flowers. that is why the common names are Proliferous Pink or Childling Pink.
Thanks, very useful. I think I had only seen the young flowers (as shown in the second photo that I have added) and did not recognise that the flower head changed as it aged.