I gotta add to this.
When my sister was very small (3-4 years or so), she wanted to sleep in my mum's bed one night. My mum was sleeping in the living room due to our apartment being tiny. She said she was scared, but couldn't explain why.
She cuddled up with my mum, and my mum was just about to fall asleep when my sister whispered "Mum? Do you see them too?
My mum froze, and looked around but couldn't see anything. She asked my sister what she was seeing, and my sister said that some weird white people were standing around the bed and looking at them. My mum, scared out of her wits, told her that it was nothing, and to go to sleep.
BTW my sister never lies, and she was too small to have given the concept of ghosts much thought, so we're sure this wasn't a prank or anything.
Then, a few years ago, my mum bought an old house, which she shared with her sister + sister's husband, our aunt and uncle. I am living with my fiancÚ, so my mother's half of the house is only occupied by her, my sister who's 11 at the time, and my brother who's 14.
There's several things wrong with this house. One of the rooms seriously need renovation, but the previous owners never got around to it. Not in the TEN years they lived there. And for the first year, my mum, aunt and uncle couldn't seem to figure out what to do about the room, no matter how many plans they tried to make for it.
They would also have meetings about the renovation of the house, but if they had the meeting in my aunt's side of the house, it would ALWAYS end in fights and disagreements. Nothing would get done. There was a corner of the room that was always really cold, no matter how hot it was outside (they thought it was maybe a broken window, but couldn't find any places that the wind could get in)
Also, in one room, where I'd sleep when I was visiting, I always slept really badly, and often had nightmares.
Anyway, everyone was getting on each other's nerves, and then my sister started seeing things. First, she freaked out because she heard an old, grumpy man mumbling in the empty room. He sounded angry and at first she thought it was the TV but when she checked, none of their TVs were on.
Later, she was looking in a mirror, and in the mirror, she saw several white, fog-like things walking past outside the window behind her. She spun around but couldn't see anything.
After a while, my sister was getting pretty hysterical, and wanted to move away, and she refused to be alone, or near the empty room. She also said that she felt that someone was looking at her through the windows, when it was dark. My mum and I were always really sensible and down to earth, and never really believed in ghosts as such, but my aunt decided to have a medium visiting. They didn't tell her ANYTHING about their issues, only that they would like her to check the house out.
The woman got goosebumps the minute she stepped inside the house (My mum noticed this) and then proceeded to walk around the entire house. In the cold corner of the living room, a little girl had drowned. In the empty room, an old man refused to let anyone change his house. And around the house, a group of people were walking around, possibly looking for the drowned girl. This is what she said, WITHOUT having heard about what my sister saw!
We were all quite freaked out, I tell you! But she told them all to leave, and then came back 2 weeks later to make sure everything was gone, and it was. The house has been fine ever since, except my aunt and uncle are getting divorced (unrelated reasons) so they need to sell the house. But nothing bad has been happening, and my sister haven't seen anything. (Note: My sister wasn't told that the medium had been there until a few months later, but in those months, she hadn't been complaining about the ghosts at all)
Also, my mum thought it was weird that a girl had drowned, because there's NO water nearby. She asked their neighbor, who runs a small museum, and he told her that the stream of water running the mill used to go right thought their house, 80-90 years ago