Ermengarde was born c. 1170 to Richard I, Viscount de Beaumont-le-Vicomte, de Fresnay et de Ste-Suzanne (died aft. 1199, bur. Etival), and wife (m. bef. 1177) Lucie de l'Aigle (died aft. 1217), daughter of Richard II de l'Aigle[1]. Her father was the son of Roscelin, Viscount de Beaumont (died ca. 1176) and wife (m. 1122) Constance or Maud FitzRoy, illegitimate daughter of King Henry I of England.

1. Margaret (1193–1259), married Hubert de Burgh, 1st Earl of Kent.
2. Isabel (1195–1253), married Roger Bigod, 4th Earl of Norfolk.
3. Alexander II of Scotland (1198–1249).
4. Marjorie (1200–17 November 1244),[3] married Gilbert Marshal, 4th Earl of Pembroke.