While cleaning out my inbox I ran across this article about a sweater knit in wool and acrylic that somehow ended up in the washer and dryer. It did shrink to the point that the neck is now too small to go over the head of a child.
Solution? Add a zipper. Check out the process used at Creative Knitting.
On a personal note, I am still too frightened of unraveling the whole thing to try this myself, but I have seen so many articles on making it work I may have to put this on my “Try It Out” list.