I have made a pair of kids leg warmer's but by switching up to larger knitting needles you can easily make them for adults also. These are sized to fit a 4 to 6 year old.
You will need:
size 7 and size 8 straight knitting needles
large sewing needle
Step 1: Time To Knit
Knit 1, purl 1 across making a rib stitch for about 2".
Switch to the size 8 needles for the body of the leg warmer's
Here is where you can be creative and use your favorite knit stitch.
I used a moss stitch of k2, p2 across then on the next row I k2 in the purl stitches and p2 in the knit stitches.
Knit in pattern until the entire piece measures 8".
Switch back to the smaller needles and rib stitch, same as the top for about 3 1/3" making the total length 11 1/2".
You can sew them up at this point and add the buttons for decoration or make a flap with 2 buttonholes so they can be buttoned closed at the bottom.