I found the idea here.
It went together rather quickly (a little over an hour, but I also had to re-teach myself how to make a chain using a crocket hook. thank goodness for youtube). I made the indicated "large" size, which was 2o inches for each side and left 4 inches in the leg openings. The leg openings were a bit snug for my hefty legged 1 1/2 year old, but worked! I loved this and am looking for any other shrunken wool sweaters I might be able to procure from our local thrift store....I want to make lots more!
This sweater had a rather wide waist and extra long cuffs, which I think worked well for the over all look. I can imagine that each sweater used could make dramatically different covers in size and appearance.
I made this to use as an actual cloth diaper cover, as the wool is naturally leak resistant (once lanolized and all that jazz), but really this would be adorable as just some bottoms to wear any old day, over any ole diaper.