
First you have to determine the length you would like the legwarmers. I compared my socks to a pair of Babylegs legwarmers that I bought for my first son. They were about 10 inches. The smaller socks I have will end up being about 10 inches and the larger socks will end up about 12 inches. 
Cut the socks in a straight line just about the heel. This will be the main part of you legwarmers. Then cut in a straight line just after the heel and before the toe, this part will be the cuff. Turn your cuffs in so that the wrong sides are together.
Turn the socks inside out and insert the cuff into the bottom of the sock. Keep the raw edges together.
Time to go to your machine. If you have a serger, then lucky you, this will take no time and look great. I don't have a serger so I back stitched at the begining and end and I did a small zig zag stitch around the whole sock. Be careful to keep the layers together or you will end up with holes.
Turn your legwarmers inside out and you are finished. I think it took me maybe 30 minutes to make all of these. Have fun making your own.
-Ashley