Constance, the ruling princess of Antioch, was eight years old when she was kidnapped and married to Raymond of Poitiers in 1136. Constance's widowed mother, Alice, was told that she would be the one marrying Raymond. Embarrassed and powerless, Alice left Antioch permanently.
Charlotte of Savoy was somewhere between seven and ten years of age when she became the second wife of Louis XII of France in 1451. He ditched his very young bride in Burgundy when acceded to the throne without money or a way back to the French court.
Maria Pia of Italy married Luis I of Portugal in 1862 just before her fifteenth birthday. She had her first child, Carlos I, just before her sixteenth birthday.
Empress Matilda (daughter of Henry I of England) had just turned eight when she married Holy Roman Emperor Henry V in 1110.
Agnes of France was about eight when she married Byzantine Emperor Alexios Komnenos in 1180.