This day Traditionally is called the ”Tango-no-sekku端午の節句”, (Boy's Festival), which is day to wish the growth of the boy in the family.
Koinobori (carp streamers) ,the symbol of strength and courage, were flown outside to tell the gods that there is a boy in the house and ask for blessings and miniature suits of armor were displayed inside the house in hope of healthy growth of the boys.
Celebrating Tango-no-sekku still remains, but Children's Day is celebrated in hope of healthy growth, happiness, and prosperity of both boys and girls.
And it is the tradition to eat rice cakes wrapped in oak leaves (kashiwamochi 柏餅） and sweet rice wrapped in bamboo leaves (chimaki -粽）. The oak leaf is a sign of prosperity as it does not fall off from the tree branch. And the chimaki comes from the tradition of throwing in the chimaki in the river as a memorial service for the deceased.
On this day we bathe in a tub with iris (shoubuyu 菖蒲湯） The iris is said to keep away the evil spirits, therefore used to be hung under the roof and used for bathing. The iris leaves also resemble a sword and was used for sword fights among children. You may have noticed the Iris flowers in Supermarkets in Japan during this season.
Actually, the Japanese name for iris, "shoubu" sound the same as the kanji ”尚武” meaning to "respect martial arts", so since the Kamakura Era, we displayed the samurai's armour or helmets to celebrate the birth of a boy.
I'm Miyuki and I teach Japanese Home cooking at my home in Tokyo.