This image is placed where it is because the oldest child, the future Leopold III (b. 3 November 1901), looks to be around 17. Even if Leopold is 14 or 18, the photo still dates to some time during or a little after World War I.
Sepia tone removed by gogm.
This photo appears be an early post-war photo based on the fluid look of Elisabeth's dress, especially the cape, and her long necklace.
Keywords: Queen Elisabeth of Belgium, Wittelsbach family, Wettin family, Princess, Queen, straight coiffure, trapezoidal neckline, cape, waist band, natural waistline, close skirt, over-skirt, necklace