Which is the first children's book in which Dr Seuss did not write in rhyming verse?

Question

Which 1936 children's book was labelled a pacifist manifesto, banned at the time in Spain, burned as propaganda in Nazi Germany, but granted privileged status by Stalin as the only non-communist children's book allowed in Poland?

Answer 1

The 500 Hats of Bartholomew Cubbins
The book was published in 1938. It was followed in 1939 by "The King's Stilts", written in prose rather than verse.