What is the name of the Japanese Children's Day--the one on which they fly fish?

Kodomo no hi, 5 May. This being Japan, although it's called Children's Day, it's actually Boys' Day. The custom of flying the fish is called koi-nobori (setting up carp) and the day is also often called this. I seem to remember that officially you fly one for each son of the house, but peopel are less rigid about this now.

Girls get a different day called 'Ohina-matsuri' - the Festival of Dolls, on March third. This is not a national holiday.

Google on any of the terms and you'll get lots of pretty pictures