Shichi-Go-San

In the Heian Period (794-1185) a ritual called Shichi-Go-San or Seven-Five-Three was developed by nobles to celebrate rites of passage for their three year old girls, five year old boys and seven year old girls.

Three - originally the age at which samurai children stopped shaving their heads
Five - Boys are allowed to wear their first hakama (samurai formal bottom wear)
Seven - Girls are allowed to wear an obi around their kimonos instead of a plain cord

The modern version of this celebration involves dressing up the children and going to shrines to be blessed with health and longevity. The children get decorative bags with crane and turtle designs as well as chitose-ame (1000 year candy) that looks like a huge, straight candy cane which is supposed to ensure a long life and probably a sugar high. :)

7-5-3 takes place at many shrines throughout Kyoto in the weeks surrounding November 15th. I went to Heian Shrine to check it out. Practicing my Japanese in "a real life setting" as recommended by my sensei, I congratulated several families on their children's milestones and asked if I could take some photos. It was really fun and the kids were absurdly adorable!
とてもとてもかわいいですね！