You will need straight pins, a band of elastic, sharp scissors, a measuring tape, an iron, fabric chalk or marker, and thread that matches the color of the pants. Most of these can be purchased from a sewing or craft store. They may also be available a large variety store.
Put on the pants and determine where the legs need to end and mark this out on the fabric. Add 2 inches to this length and mark that out as well. Cut along this 2nd line for the bottom edge of the pants.
Turn the pants inside out. Fold over the bottom edge of the pants leg 1/2 inch against the wrong side of the fabric, using the measuring tape and the marker, and press it down with the iron. Fold that over again along your first line. This will create a casing for the elastic. Press this down. Insert straight pins to hold the casing in place.
Sew slowly and carefully along the upper folded edge of the pants. You can just go ahead and use the regular stitch. Leave about 2 inches a unsewn on each casing seam. This will be where you will insert the elastic.
Measure loosely around your ankle where the elastic will go. Divide that measurement by two and add 1 inch, cutting two pieces of elastic this length.
Insert a safety pin into one end of the elastic. Put the closed safety pin into the opening of the casing, anchoring the other end so it won’t get pulled all the way through. Feed the safety pin connected to the elastic through the casing until it emerges from the other side. Grasp both ends of the elastic and overlap them together with a straight pin. Stitch two parallel lines across both the overlapped ends with the sewing machine so they are held together. Release the elastic into the casing.
Finish sewing the rest of the casing seam closed.
Thanks! It looks like your plan will work. I appreciate it.