Anne Frank is the little girl to the left (in a dress in the front row). Margo Frank, Anne’s older sister, is with the taller kids in the back row, and is wearing a dress similar to her sister’s. Margo is the one on the right. Both Anne and Margo died of typhus at Bergen-Belsen Concentration Camp in March, 1945. Bergen-Belsen is near Hanover, in northwest Germany.
Here’s an image from Bergen-Belsen (taken in 1945):
Source for both photos: U.S. Holocaust Museum Photo Archive