Japanese Sweets - Why Kashiwa Mochi on Children's Day?

On April 13, 2018, I bought kashiwa mochi, a seasonal rice cake delicacy, at Minamoto Kichoan on B1 of at the Ginza Matsuya Department Store. Kashiwa mochi is a Japanese traditional sweet wrapped in a kashiwa, i.e., oak, leaf, eaten on the Children's Day (i.e., May 5) to hope the continuity of the family. The tradition started during the Edo period based on the fact that oak leaves don't fall until the new ones come out. I got two types of kashiwa mochi, one is with koshian, i.e., red bean paste whose texture is smooth because the paste is sifted to remove bean skins, in it and the other is with tsubuan, i.e., red bean paste whose bean texture is more perceptible because the paste is not sifted. Surprisingly, the confectionery has outlets in not only Japan, but also the U.S., the U.K., and other Asian countries. So, if you can buy this mochi sweet in Japan or somewhere else on around May 5, the Children's Day, I recommend eating it to enjoy the flavor of a fresh oak leaf. The size of the sweet varies between confectioneries and those I bought were a little smaller, but their taste was worth four stars.