This is a quick demo of my test rig for Squash and Stretch. I use OOO and effectors to get cleaner effects and an easier setup. I also built it as an assembly utilizing weight containers to switch out meshes more efficiently. Originally I parented meshes to a target locator. Although that worked out fine, the weight containers are ultimately more flexible to use in complex setup.

The rig is provided in the Luxology share site...with my son's animation included...

Have fun and feedback would be greatly appreciated!