While this might be something you'd want to play on your friends, especially the really rude ones, but please don't do this to any kids -unless you want to get an Easter basket filled with dog turds next year.
I did something similar a couple years ago. Mine involved putting egg inside an actual Cadbury. No one got upset. The tutorial is here: http://teemingswarm.com/2010/04/10/the-ghost-of-salmonella-future/
That was you last year!
I've always suspected....
http://teemingswarm.com/2010/04/10/the-ghost-of-salmonella-future/