Jason was ready to retire an old 0 degree down bag.  The zipper was bad off at the top and he was ready for more loft.  I drew a concave line on the upper top (red side) and a convex line on the upper bottom (black side) of the bag with a Sharpee.  These lines were around1.5 feet from the top of the sleeping bag.  This length was determined by how long I wanted the bag and how much I needed to cut off to get rid of the bad part of the zipper.  Then I sewed along this line twice to lock the down in to the lower part of the bag.  Taking the bag outside to the trash can, I cut 3 inches above these lines.  Too bad it was a windy day - the yard did look a little "goosey" afterwards.  Then I rolled the three inches down over itself (both layers of nylon) and sewed just about on the original line.  This created a casing to thread in elastic and also made the upper edge nice and clean again (not really nice, it is hard to sew neatly with nylon, and errant feathers).  I used elastic rather than cords since I didnt think it was a good idea for a toddler to sleep with cords near her neck.  The elastic also makes all the tucks and wrinkles of the sewing job "disappear".  I added a button at the top of the zipper to hold it closed.  Violet is about 30 inches tall and the bag will likely fit her for another two years. Check out Winter Sports for a detailed picture of the opening.