'Seven-five-three'. A festival held on November 15th, or very often these days on the nearest Sunday to make it a two-parent occasion. It is one of the life-cycle rites connected with the ujigami in which girls of three and seven and boys of five (sometimes three and five) dress in their best and brightest clothes (hare-gi), often traditional kimono, and visit their local or ujigami shrine with parents. The visit takes place either on the festival day or sometime during the month. The children take part in a rite for their own protection and future good fortune. Like miyamairi, shichi-go-san has been growing in popularity in recent years. The origin of the rite is unclear but it is perhaps related to old customs surrounding the first wearing of traditional garments such as hakama for boys and obi for girls. The custom is particularly popular in the Kanto area (around Tokyo). Shichi-go-san also takes place at some Buddhist temples.
A Popular Dictionary of Shinto. Brian Bocking.