How did the children of Varina Davis die?

Varina Davis, the wife of Confederate President Jefferson Davis, lost her children to various illnesses. Their son, Joseph Emory Davis, died in 1854 at the age of 2 from pneumonia. Another son, William Howell Davis, died in 1864 at the age of 21 from complications related to tuberculosis. Their daughter, Margaret, also passed away in infancy in 1864.