Not Mom jeans. But technically. My Mom's jeans that landed in the donation bin because they never did fit her right. For some reason she didn't recognize them when they came walking in her front door one day...
So they started life like this. I traced around the legs of a pair that fit me well.
Pins and the marker line, this is the outside of the leg. Sew along that line, trim and zigzag the raw edges.
Try them on and pin the inside curves. Leave lots of ankle room, as I learned the hard way the very first time I tried this. Take the pants off with comical slowness as your husband laughs at you for hopping around the living room in your underwear, half out of pin-filled pants.
Sew and finish the inside seam, flip them right side out and there you have it.
Brand new skinny jeans.
Hopefully it goes without saying that you need to start with a pair of stretchy pants for this! Or avoid eating, and preferably breathing as well.