There is some literature on this. Recently, this was taken up in two articles in the collection edited by Peter Narvaez, The Good People: New Fairylore Essays (Lexington: University of Kentucky, 1997). The one more often cited is by Susan Schoon Eberly, "Fairies and the Folklore of Disability: Changelings, Hybrids, and the Solitary Fairy. There is also an article by Joyce Underwood Munro, "The Invisible Made Visible: The Fairy Changeling as a Folk Articulation of Failure to Thrive in Infants and Children." This idea was not new when they gave voice to it: Elisabeth Hartmann discussed it in her masterwork: Die Trollvorstellungen in den Sagen und Märchen der Skandinavischen Völker (Tübingen: Eberhard Karls Universität Tübingen, 1936).

I discuss some of this in my forthcoming title: The Folklore of Cornwall: The Oral Tradition of a Celtic Nation.

In Cornwall - to consider the question in a micro-setting - there are numerous accounts of children who failed to thrive for a variety of reasons and were thought, consequently, to be changelings. Parents (and helpful neighbors!) were drawing upon a common Northern European Migratory Legend (which appears among other places in the Grimm collection) that describes various means to force the supernatural entities to bring back the human infant in exchange for the changeling that they have left. Those means too often called for the ill-treatment of the poor baby, and there are accounts that describe how people tried this approach so they could have their "real" infant returned. Of course, the instances where these tragedies occurred never effected the return of any infant, because the parents were dealing with a developmentally-challenged child.

Others have found much the same thing. One of the conclusion that is obvious is that certain situations recalled the idea that supernatural beings desire to have human infants and will exchange one of their own for a healthy human baby. Parents with a developmentally-challenged baby would recall the stories they had heard (or neighbors would be happy to share!), telling of this propensity of supernatural beings, and the parents too often acted accordingly. So did people make a connection between the stories about changelings and their own situations? Clearly, the answer is yes, but that is not precisely what you have asked.

Your question is whether autism or other developmental disabilities inspired stories about changelings. That is more difficult to answer, and I am inclined to say no, although certainly real-life situations may have affected the legendary material - and even encouraged it to spread.

The supernatural beings who were thought to abduct infants also sought to abduct women right after childbirth. In addition, there are stories from elsewhere about supernatural abduction of infants that do not involve these sorts of developmental issues. The Northern Paiute of the Great Basin, for example, tell a story about the paúngaa’a. Here, I'll excerpt from my Introduction to Folklore:

In North America’s Great Basin, Northern Paiute tradition includes the paúngaa’a, which translates as “water baby,” a name that does not match the sinister quality of the creature. This ruler of the water plays an important role in a testimonial legend that tells of a woman who left her infant in a cradleboard by the water while she gathered edible plants. She hears her infant crying, and so she returns and attempts to suckle the baby. When the baby opens its mouth, it reveals huge fangs, and it bites into the breast of the woman. It is, in fact, the paúngaa’a, which has devoured the baby and is now chewing on the mother. The woman must quickly summon a shaman with paúngaa’a power to chant the demon away. The supernatural being responds by retreating back into the water. This legend warns about the dangers of the water and about not being an attentive mother.

In this case, the baby simply reveals itself to be a vicious demon - something that real-life certainly did not inspired.

People often attempt to find the "real-life" situation or historical character/event that inspired folklore, but my experience, it does not work that way. Northern Europeans have a broad range of stories about supernatural beings who sought to be with humans - and "be with" often involved abduction. The stories describing these situations more often than not as simply involving the person being in the wrong place at the wrong time. These entities were dangerous for many reasons, not the least of which was that they would steal people of a wide variety of ages. One really cannot link all these stories to a core, "real" circumstance of the human condition.

That said, people who knew these stories often applied them to their own situation, often with devastating results. The 1895 instance of "The Burning of Bridget Cleary" (see the book of that title by Angela Bourke), describes how a woman became ill, and her husband decided that his real wife had been abducted. He subsequently burnt what he thought was a changeling, but his act failed to inspire the fairies to return his wife. He buried the remains, was subsequently found out, and was convicted of murder by a UK court that had little sympathy for a rural manifestation of folk belief. Mr. Cleary was responding to a body of folklore; but the other side of the coin was that the circumstance of his wife did not inspire the idea that the fairies sought to abduct people.

Of course, real-life circumstance affects folklore. Not only did people use the legend and notion of changelings to help them understand a developmentally-challenged infant, but those real-life examples likely reinforced the changeling tradition. So there was, indeed, a give and take between reality and folklore. But concluding that this specific circumstance was the point of origin of the changeling legend would be taking it a step too far, in my opinion.

I hope that's not too muddled.