As requested -
In Celtic folklore there is something called a changeling related to the Fae. Basically a changeling child was believed to be born of the Fae (Fairy child) which had been swapped for a human child by the fairies.
It is very common in Fae literature and also aligns itself with children thought to be afflicted with disorders or developmental disabilities.
Following a brief Google search I found –
“The reality behind many changeling legends was often the birth of deformed or developmentally disabled children. Among the diseases with symptoms that match the description of changeling in various legends are Spina bifida, Cystic fibrosis, PKU, Progeria, Down syndrome, Homocystinuria, Williams syndrome, Hurler syndrome, Hunter syndrome, Regressive autism, Prader-Willi syndrome and Cerebral palsy.
The greater proneness of boys with birth defects correlates to the belief that male infants were more likely to be taken.
It has been hypothesized that the chandelling legend may have developed, or at least been used to explain the peculiarities of children who did not develop normally, probably including all sorts of developmental delays and abnormalities.
In particular, it has been suggested that children with autism would be likely to be labelled as changelings or elf-children due to their strange, sometimes inexplicable behaviour.
For example this association might explain why fairies are often described as having an obsessive impulse to count things like handfuls of spilled seeds.
This has found a place in autistic culture. Some autistic adults have come to identify with changelings for this reason and their own feeling of being in a world where they do not belong and of practically not being the same species as the other people around them.”
It was said that you could “trick” the changeling into doing/saying something that shows that it isn’t really a child.
I found a story about an autistic boy who is virtually silent most of the time, and the things that he does say are usually difficult to understand. However, he builds incredible lego mansions and fortresses and builds them taller than he is, with attention to colour and detail that seem far beyond a child of his age (7).
In history gone would it would be very easy to see a child similar to this where parents or family might see their “dumb” child doing something very advanced or gifted and think that they have “caught” the changeling out.
So, were the changelings real and children of the Fae? Or did disorders such as autism play a major part in creating myths and folklore such as this one.