The thumbnail summary of the 1940s was from knickers to jeans for the American boy. Knickers began to become less popular during the late 1930s. They were still worn in the early 1940s, but were quicly passed from boys' wardrobes. Smaller boys wore shorts, but most older boys who had worn knickers now wore long pants. Boys who did wesr short pants suits often wore ankel socks, except for wealthy or well-to-do families that were more intunded with English fashions.
The war in Asia had a significant impact on womens's fashions. Shipments of silk were cut off. This gave a great impetus to the production of sythentic fibers like nylon which would eventually filler through to men and boys' fashions. Shortages of wool gave impetus to research into regenerated protein fibers. One result was the milk protein fiber Aralac. It made the advertising pages of Vogue, but consumers complained that when it got wet it smelled like sour milk.
Fashion including children's clothes was constrained by the War. In 1942, "General Limitation Order L-85" placed restrictions on the quantity of fabrics used in apparel. With the exceptions of infants' and toddlers' clothing, bridal gowns, maternity dresses, burial gowns, and clothing for religious orders, regulations detailed a wide variety of specific restrictions on the cut of women's and girl's apparel. It limited the width of hems, abolished cuffs, and eliminated wide belts. Gone was the suit for men with two sets of trousers, and vests could not be sold with double-breasted suits. Extra pockets were abolished, as were pleats in trousers. The War did create one new fashion that would come to dominate boys' and eventualy girls' leisure wear. World War II also witnessed the birth of the "t" shirt. A part of military dress, this undergarment went on to a long civilian life after the war, and beginning in the late 1940s a "t" shirt with bright colored horizontal stripes became a main stay of American boyhood fashions. Most boys lived in "t" shirts, jeans, and Keds (sneakers). The L-85 regulations had the effect of "freezing" styles throughout the wartime period and beyond. Although the war ended in 1945, it took time for scarce textile products to come back to the market.
Some consider the post-war 1940s among the best kept secrets of our time. World War II was not an important factor in most boys' lives. Unlike Europeans, American children were far removed from the war, except for day being away. The aftermath of the war was a different matter. The primary influence from it was a huge back to the home movement. Women were to stay home and have babies, support their husbands in their careers and that was all. There was a drastic change in women's clothes. I remember "The New Look" with long skirts and leg of mutton sleeves. Surburbia really took off. Teenagers rejected Boogie Woogie and returned to Big Band sounds. Girls wore strapless taffeta gowns and spectator pumps. The boys all had those jackets with the velvet collars. I have forgotten what they were called. They wore white shirts and the mothers complained a lot about having to iron them. American boys and teenagers virtually lived in their jeans, wearing them every where that they could get away with it--but almost never in high school. Teenage boys wanting to look "cool" wore them low on the hips with the new hair fashion--crew cuts.