First step-- Take a large white v-neck t-shirt and cut it up the front. If there is a problem with it rolling, just iron on some fusible interfacing. If you are wondering what size we used on our shirt it was mens large.
Then let the kids loose to decorate the back. The boys just used fabric markers to decorate them.
Once you have finished drawing a design then the kids get to wear them. To tie the Komono up use some fabric strips to tie it up. The tie is called an obi. How to tie the obi. Wrap the Kimono closed with the left side over the right. Boys tie a narrow sash in the front. Girls tie a wide sash into a flat bow in the back.