I have a theory that the folk tales of changelings - babies being stolen by and replaced with fairies - are probably sparked by children with autism in the past. From what I understand, sometimes a child can seem to be developing neurotypically for a long time before developing symptoms of Asperger's or autism pretty suddenly.

If you're a farmer in 1400, your child suddenly stops being communicative, and effectively turns into a different person. Obviously fairies did it.