My cousin was born years after the death of what would have been their older sibling who died as an 11 year old.
It was very much the done thing in our (Asian) family at the time to not talk about the older child or their death, their name, nothing. There was a lot of superstition around a child's death.
The youngest sibling began expressing that they used to be the older (opposite sex) dead sibling before they were born, accurately describing events and memories that they "remembered"from the dead sibling's perspective and which no one had ever mentioned. Including the illness that ended their life. This "remembering" all began as soon as they could talk and they were very insistent.
I.e "Mummy, I used to be a girl didn't I?"
"I was a girl called Anna. Don't you remember when I was Anna? And grandad used to take me to the lake and tell me about the fish? WHY DON'T YOU REMEMBER ME BEING ANNA MUMMY?" (Grandad died years before they were born).
"When I was a girl, Mummy, I was scared and you would cry. I would lie on that couch and there would be blood (their sibling died of blood cancer) and I would cry and you would cry. You'd say I'd be ok but I'm a boy now and I want to be a girl again and it's not ok. I liked being Anna Mummy, why am I a boy now and you all call me the wrong name?"
It went on for about three years (strongest between ages 2 and 5), along with intense gender issues, massive temper tantrums and all sorts of disturbing issues. Then one day it suddenly all stopped and they never referred to it again.
They're an adult now and have no recollection whatsoever. It was utterly,
utterly chilling at the time.