As can be seen in the Chigo daishi zu (a late Kamakura work owned by the Kayuki Art Museum) and other such illustrations, children's kosode during Japan's medieval period was made with furi-no-yatsuguchi in the sleeves to allow body heat to dissipate.
稚児大師図（香雪美術館蔵・鎌倉後期）などに見られるように、子供の小袖は中世の時代は体温を逃がす振りの八つ口をあけていた。