When Son 3 was 2 or 3 years old, we went on holiday in the county where I grew up and took a detour to see my mum's grave, in the churchyard of the village where I grew up. This was 150 miles from where we lived and Son 3 had never been there before (or his older brothers).
Behind the church is a field, which has 'The White Lady Pond' in it. A standard UK 'white lady' is said to haunt the field, rising out of the water. Kids still re-tell the story. We used to tell it in the 1960s...
I hadn't ever particularly felt the need to talk about this with anyone although I would have told husband the White Lady story. Years before Son 3 was born, no doubt.
Anyway, we said 'hello' to my mum's grave then walked round the back of the church. Stood and looked over the field with the White Lady pond.
Son 3 took one look at the pond and said "Is that where the Lady With The Long Hair lives?"
Shat me up for weeks after. I knew it was not something he'd heard from us. Or anybody 150 miles away!
Son 1 and I took a shortcut through a cemetery, to school every day. In the cemetery he started wandering off a bit on the way home - not out of my sight, just going off to play alongside kinda thing. Turned out he had an imaginary friend. I asked who it was and what they were like.
"Oh, it's a little girl my age in a wheelchair!"
Random, I thought. Another time I asked him where he first saw her. He pointed to a certain area. The children's gravestones.
FFS.