Number of photos doesn't show in parent folder

The parent folder doesn't show the number of photos than are in the subfolders, which has as a consequence that you can't have a list of marked pictures in all the subfolders at once. This is what I see:

Parent folder: "All my photos    0"

Subfolders:          "Animals      22"

                             "Family        45"

                             "Landscapes 12"

                             "Flowers       23"