Having never made a kilt before, I immediately searched for help. I found this excellent video tutorial showing how to make a very simple kilt and was saved. Since I can barely sew a straight line with a machine, this is right at my skill level.
I found a nice Tartan with a 4 inch repeat. Instead of cutting in half, I cut them to the width I measured for each kid (from waist to knee). I also measured them across the front and adjusted the width of the front panel for each kid. The smaller repeat made the pleats smaller and more suitable for a child's kilt. When making the pleats, I simply followed the repeat of the plaid. Unlike the video, I starched and pressed each pleat as I made it.
So for a kid with a 24 inch waist, I started pleating after 10 or so inches and made inch-wide gaps between each pleat following the repeat until I had 14 pleats. That's 10 inches of smooth fabric for the front and 14 inches of pleated fabric to circle the rest of the body. After that I draped the rest of the length up over the shoulder and belted.
Add a few large safety-er- I mean kilt pins and a belt around the waist and my boys were a pair of stout Scottish lads.