Shortest Horror Stories (True Story.)
The toddler always sat on that same step chattering away to himself.
One day I asked, "Who are you talking to?"
"Amelia." he answered.
"Who's Amelia?" I asked.
"Oh she lives in the wall." he replied and giggled.
Image mine and this was a conversation between me and my then 3 year old son.
(After we moved out of the house we found out the new owners had to have the house blessed, seems Amelia didn't like losing her new friend.)

I have memories of speaking to my "imaginary friends" but it turns out that some of them actually had a little history in the old houses that I visited. I don't remember what age I stopped seeing or hearing them, but I do believe they exist.
I believe in ghost for sure. I used to see ghosts and angels when living in the haunted orphanage house in Korea at younger age around 3 to 5. Upvoted.
I think children can see these things that as we get older we lose the ability to see.