May 5th is Children's day, also called 端午の節句 (boys festival). During this day, people celebrate the happiness of all children and their healthy growth. It is a National Holiday since 1948.
Families with boys often display a helmet replica or samurai dolls at home and fly 鯉のぼり carp streamers outside.
Tradicional foods during this day are 粽 (a rice dumpling wrapped in bamboo leaves) and 柏餅 (rice cakes wrapped in an oak leaf with sweet adzuki beans inside).
In Japan, Children's day is celebrated twice a year. ひな祭り(hina matsuri) on March 3rd for the girls and こどもの日 (kodomonohi) on May 5th for the boys.