Jean Baptiste was the son of Sacagawea, a Shoshone, and her French Canadian husband Toussaint Charbonneau, the former who worked as a guide and interpreter for the Lewis and Clark Expedition. Jean Baptiste was born at Fort Mandan in North Dakota. In his early childhood, he accompanied his parents as they traveled across the country. The expedition co-leader William Clark nicknamed the boy Pompey ("Pomp" or "Little Pomp"). After the death of his mother, he lived with Clark in St. Louis, Missouri, where he attended St. Louis Academy. Clark paid for his education. Sacagawea and Toussaint Charbonneau also had a second child, a daughter named Lizette Charbonneau; however, because she receives only occasional mention in Clark's papers, her life remains unclear beyond her third birthday.