I made a pair of bloomers from some pants of mine I had already made a while back. This mod will work with stretchy material [like the type I use here] or whatever lightweight fabric you may have.
Here are the steps I took:
I cut the pants off at 22" down from my waist and over locked the raw fabric edge at the knee. Since the fabric was stretchy I pulled it taught while applying a zig zag stitch and it makes the edge very curly as you can see here.
I marked all about the circumference of of the knee , inside out of course. I marked the pants inside every 1/4 of the way about & 3" from edge for elastic.
Here you can see how it appears after applying the elastic, make sure you pull the elastic and fabric tightly to achieve this.