A little cardigan of Breanna's had a stain on it which refused to budge despite my best efforts, so before tossing it I decided to take off the zipper which was perfectly reusable.
Use a nice sharp razor blades, lock the children in the closet until you're done, and carefully cut through the stitches that hold the zipper in place.
As soon as you've gotten a little bit of the zipper worked loose it's easy to separate it from the fabric by giving it a gentle tug and then a swipe with the razor blade at the revealed stitching.
Swipe away until your zipper is free!
(Hmmm, that doesn't sound quite right, does it.)