The fun thing about these pants is you can choose your kids' favorite character or color and make them pants that they will really love! I usually make each of my kids at least one pair of pants each year with this method. They are light weight, easy to scrunch up into a tiny ziploc for travelling purposes, and most often chosen from my kids' wardrobes.
To start, find a pair of your kids' pants that fit them now. I usually try for something with a slightly wider leg and an elastic waist. For a 5 year old and under, 1 yard of your desired fabric is good, for older, you need 1 1/4 - 1 1/2 yards of fabric.
Take the fabric and fold it in half width wise- right sides facing. Turn the pants inside out, fold them in half along the crotch area, and lay them flat close to one side of the fabric. Trace, leaving about 1/2 " on the sides for the seam, 1 1/2 " on top for the waistband and another 1" on bottom for the hem. Then flip them over and trace again-leaving the same allotments for waist and hem.