According to wikipedia, the Lincoln children:
Thomas Lincoln known as "Tad" (1853–1871), died of pleurisy.
Tad's remaining years after his father's death were very tragic. After Lincoln was assassinated, Mary Todd kept Tad locked up in a room with her while she mourned and wept. Rather than being able to mourn the death of his father, he had to comfort his mother, when it should have been the other way around.
On a more positive note, I saw the film this past Monday, and loved it.