What year was the first children's book published with Dr. Seuss as the author?

Theodor Seuss Geisel ( March 2, 1904 – September 24, 1991) was an American author, political cartoonist, poet, animator, book publisher, and artist, best known for authoring children's books under the pen name Dr. Seuss. His first book was And to think that I saw it on Mulberry Street. It was published in 1937.

Geisel wrote four more books before the US entered World War II. These included The 500 Hats of Bartholomew Cubbins in 1938, as well as The King's Stilts and The Seven Lady Godivas in 1939, all of which were in prose, atypically for him. This was followed by Horton Hatches the Egg in 1940, in which Geisel returned to the use of poetry. During World War II Geisel made political cartoons.

Some of his most famous books include: Horton Hears a Who! (1955), If I Ran the Circus (1956), The Cat in the Hat (1957), How the Grinch Stole Christmas! (1957), and Green Eggs and Ham (1960). He published over 60 books during his career, which have been made into numerous adaptations, including 11 television specials, four feature films, a Broadway musical, and four television series.