This is how you can very simply (and without buying a pattern) turn an old pair of men’s athletic shorts into some sporty pants for your toddler.
Start by laying out a pair of your toddler’s pants on top of the shorts, like in the picture below. Pin in place.
Using the pants as a guide, cut the same shape from the shorts. Don’t cut the outer leg seam- no reason to make more work for yourself. (I cut the pants quite a bit bigger, partly for the seam allowance, but also because my son is growing out of the pants and I wanted the new athletic pants to fit for a while. I went back and cut the waistband smaller, though, since it already has elastic in it.)
Using the leg piece you just cut out, cut the exact same thing on the other side.
Below are both leg pieces spread out and stacked, right sides together. The top left and right angled seams are pinned- sew just from the waistband to the pointy part, and that becomes the crotch seam.
Match the two seams you just sewed together, still with right sides together. Pin the inseams and sew. The bottom is already hemmed, and the top is already finished with elastic. You may need to tailor it a bit to your child’s waist size.
20 minutes from start to finish, and your little one has some sporty new (free) pants!