When my sister visited us July 4th weekend, my 5.5 year old son (who is eg/pg) told her that he heard voices in his head and asked if she did too. My sister, who has Asperger's, kind of panicked because she thought of one of our aunts, who has schizophrenia and exceptionally gifted (IQ 165). I told my sister not to worry about it; at the time I wondered if my son had advanced metacognition but I didn't want to go into a discussion with my sister about it.
Of course, if you start talking about this kind of stuff with family, neighbors, or people at your child's school, they may start looking at you funny and question it and wonder whether your child is a future candidate for mental illness. It's a bit awkward to talk about.
So now I say thank you very much for bringing this up. Our children have a gift - advanced metacognition.
