On this day, every girl and boy dresses up for the ceremony called "seijin-shiki"(成人式), coimg age ceremony in English. Generally, girls wear a "furisode"(long sleeved kimono) and boys wear a suit or a hakama.
Here you can have a look at the atmosphere of "seijin-shiki."
Even for us Japanese, wearing a furisode or a hakama is very rare and a very special experience.
In this January, I actually experienced my coming age ceremony and wore my furisode, which was made by my grand mother, who is very good at sewing. I've worn kimono, but this was the first time for me to wear furisode. When I finished wearing it and looked at myself in the mirror, I felt tensed and refreshed. While I was walking outside with it, I could keep a good posture and being a graceful in manner.
You guys also have a chance to wear a kimono or a hakama in Kyoto! If you google the word "kimono, rent", you can find the place where you can experience kimono, its price, etc. You can choose your favorite color, types of kimono and hair styles! Also you can walk around Kyoto by wearing a kimono and visit some temples. Those experiences will make you enjoy Japanese atmosphere!