"All the Smurfs that existed in the generation that Papa Smurf calls "my little Smurfs" WEREN'T entirely his! They were created by other Smurfs that have existed in Papa Smurf's generation (his "fellow Smurfs"), and those Smurfs consisted of both male AND female Smurfs, who were basically called Papa Smurf and Mama Smurf by the children they produced. The Smurf who became the Papa Smurf may have been responsible for fathering at least one of the children (possibly Brainy!).

"So what happened to all those male and female Smurfs that created those wonderful hundred little Smurfs? They either all died off from some unknown disease that Papa Smurf and the young Smurfs were immune to, or somehow mysteriously vanished. There might have been a curse placed on Papa Smurf's generation that if he and his fellow Smurfs should ever sire only male children, the parents would eventually cease to exist.

"Of course, this could have happened when the young Smurfs were Smurflings and most of them had very little understanding of how to survive on their own without parents. So as the Smurf who became the Papa Smurf survived while his fellow Smurfs died off, he took it upon himself to raise the hundred orphaned children as his own, fully adopting the identity of Papa Smurf. Over time, the hundred orphaned young Smurfs let go of the memory of their deceased parents and accepted Papa Smurf as their father.

"However, Papa Smurf had to find another group of Smurfs that had females among them so that his "little Smurfs" would become parents of a new generation. While he has not been entirely successful in doing so yet, Papa Smurf had transformed two artificially-created female Smurfs into real Smurfs -- the adult Smurfette and the Smurfling known as Sassette."

However, I'm pretty sure the Stork brings new little Smurfs!