Who was Lincolns oldest son and the only one to survive to adulthood?

Thomas "Tad" Lincoln. (April 4, 1853 - July 15, 1871) He was named for Lincoln's father, Thomas Lincoln, but upon his birth, Abraham remarked that the baby's unusually large head made him appear like a "tadpole." The name stuck, and Thomas was called "Tad" or "Taddie" for the rest of his life.