The Ed, Edd and Eddy purgatory theory is about the kids living in a state where they never grow older in as much as they keep living and that even when they die, they will still remain as kids. It is about all the kids in the shoe dying and going into this other world where they remember nothing about where they came from. Read more about it on http://www.tumblr.com/tagged/purgatory-theory.
The theory basically states, that all the kids in the show died at some point in american history, and their behaviour reflects how they were raised. Not to mention how the Charectors toungs are the colour of a dead person's tounge... And in responce to r0sesarered, you could easily say that about any show; in south park, the kids never age, in family guy, they never age. The simpsons, Spongebob- just about any show that is popular, there is no continuality; The theory about spongebob's charactors being just mutated creatures due to the nuclear testing at the location in the show (AKA bikini bottom being Bikini Atoll, where, long ago, the united states and allied countries tested many nuclear bombs, has some weight to it.