Historians tell us comic books have existed since before the Victorian Era but nobody noticed them until Superman appeared in 1938.
Seven years later editor Jack Schiff reasoned that a series featuring the gamechanger's childhood would appeal to young readers. Superboy appeared in multiple titles until he was finally given his own book in 1949.
Thor's boyhood only lasted for 15 pages, spread out over the JOURNEY INTO MYSTERY #100, 101 and 102 episodes of Tales Of Asgard.
Comic Historians still haven't located any Viking comics from the 9th century...