I was aware of and had seen examples of Post-Mortem Photography. What I was not aware of was how common a practice it was in nineteenth-century America. It is in fact the largest group of nineteenth-century American genre photographs. Babies and children who had died were dressed and posed as if sleeping or dressed in their Sunday best and posed sitting on the edge of their bed or sitting in a chair.
PBS article and photogallery.
Essay: The Quickening of the Dead and the Dying of Death: Postmortem Photographs from Nineteenth-Century America.