This theory posits that the kids who inhabit the Cul-de-sac are actually dead in reality and that the lives they lead there actually take place in a purgatory-like setting.
According to the theory, the children of the cul-de-sac each hail from different eras spanning the early 1900s to the early 2000s. This would explain why the year for the show is very hard to pinpoint, with multiple anachronisms present, and also why there aren't any adults in the show (although you do catch a glimpse of one every now and then).
Rolf arrived first from the 1900s, the theory goes. His family had moved to Peach Creek in order to establish a farm on its land. Rolf died around 1903 when his family's farm animals stampeded and trampled him. This was the supposed reason as to why he only has one cow, one goat, a few pigs, and a few chickens (not enough animals to cause a fatal stampede) in the afterlife.
Johnny 2x4 came to the Cul-de-sac not too long after Rolf's death. Having no friends, Johnny took a marker and drew a face on a piece of wood, and dubbed it Plank. He died in 1922 after fighting a long battle with tuberculosis, 6 years before the discovery of penicillin. He took his friend, Plank, with him in the afterlife since he was the last thing that he saw in life before he died. Purgatory would also explain Plank's occasional sentient behavior, which is most notably demonstrated in the movie.
Eddy came next. He was born in New York but eventually moved to Peach Creek during the Great Depression era. Always trying to get a quick buck, he always set up scams to get money from the Cul-de-sac kids in an effort to escape the poverty he spent his whole life in. Eddy didn't have a proper father figure since his real father abandoned him and his mother shortly after he was born. With this, came the big bro he adored and idolized so very much despite the latter's abusive nature. After one of his scams went awry, Eddy was chased by the swindled children of the Cul-de-sac, and ran to the lake and jumped into it. Eddy ended up drowning in that lake, and he soon joined the other deceased children in the afterlife. Even though he was no longer alive, Eddy still tried to chase after the "Almighty dollar" by continuing his swindling nature in the afterlife.
Ed and Sarah were the next to arrive at the Cul-de-sac. Their father had died fighting in WWII, and as a result, thePost too long. Click here to view the full text.