Steph, Utah, USA
This started when my uncle got engaged to his girlfriend and they searched for a bigger house to accommodate the two of them, his three sons, her son, and my sister who was staying with him at the time.
They found one that was perfect, nice and big and in their price range. The one drawback is that the house was old and as the owner said "Haunted by three young children". My uncle's fiance is a psychic/medium type person and had no problem with it so they got ready to move in.
Throughout the move there were many occurrences of laughing, giggling, running footsteps from the top floor. The first time my sister took me to this house, I got chills just from looking at it, she pulled around to the back to park the car and I looked up and saw a very very old tree house... the tree house was up very high and the wood was decaying, it was kind of like a big open deck, only at the top of a tree. It gave me the creeps really bad.
Things continued in that way, just footsteps from time to time, giggling, children's voices during the night. Tapping on the windows outside. It was certainly a haunted house.
My sister has a son, that at this time was 3 years old. He started talking to people in his bedroom and when asked who he was talking to he said "My friends" then after a while... he became terrified of his bedroom and started sleeping in my sister's bed every night.
One day when I was over there babysitting I sent him in his room to get a book to read he went in there and just started screaming, when I ran in and got him he told me his friend hurt him.
I told my sister she needs to keep him out of that room, something in there was hurting him, so she did, and brought all his clothes and toys into her bedroom until we could figure out what to do about his bedroom.
A week or two later while the two of them were in the kitchen eating breakfast, her son was staring out the window at the tree house for a long time without saying anything. She told him to hurry and eat because they had to get going. So he took a few bites of cereal and said "Mommy... Nicholas is scared." She looked at him, concerned... He didn't know anyone named Nicholas. "Why is he scared?" she asked. He looked back outside at the tree house and said "He climbed into the tree house, and he fell down. Nicholas is bleeding." After he said that he looked at something next to the back door that my sister couldn't see and he became terrified.
Needless to say we never made him go into his room again and my sister moved out of there not too long after that.
That room is now inhabited by my cousin's friend that is staying in their house, yes, my uncle and them still live there to this day.