That's not correct. Population growth increased from the 1930s compared to the 1940s, and accelerated during the war (it was eg twice as high in '45 and '46 as '33). The great depression had a much greater impact on population growth than WW2 did. The only negative modern year being 1918 (combination of WW1 + deep recession post war + flu pandemic). Live births also increased during WW2.