The flower corsage they are wearing are called "mums." There is a silk chrysanthemum flower in the center and lots of ribbon attached. The ribbons have their names spelled out in stickers. The girls pin the mums to their shirts. The boys have a garter so they can wear it on their arm. The ribbons have little bells attached so you can hear them as they walk around.
This is a true southern tradition, although I hear that they are starting to make their way north and west.