The day was originally called Tango no Sekku (端午の節句), and was celebrated on the fifth day of the fifth moon in the lunar calendar or Chinese calendar. After Japan switched to the Gregorian calendar, the date was moved to May 5. It was originally exclusively male celebrating boys and recognizing fathers, but has since been changed to include both male and female children, as well as recognizing mothers along with fathers and family qualities of unity.
Until recently, Tango no sekku was known as Boys' Day (also known as Feast of Banners) while Girls' Day (Hinamatsuri) was celebrated on March 3. In 1948, the government decreed this day to be a national holiday to celebrate the happiness of all children and to express gratitude toward mothers. It was renamed Kodomo no Hi.