子供の日/Kodomo no Hi means “Children’s day”
It is celebrated on May 5th.
It’s a part of the “golden week” holidays, where lots of national holidays are bunched together to give long weekends to relax and enjoy time with your family.
It was originally just for boys (as girls have the Hina Matsuri in March) but now it is for all children.
It’s signified by the large carp flags called koinobori.
The large carp represents the father, next is the mother and the children are shown by smaller carps below.