This is kind of a long and weird story that lasted for about 4 years.
When my little sister was 2 (we are 11 years apart) she started seeing a man in her room. Being so young, I know she couldn't make this up and was not exposed to anything that would allow her to even know what a spirit was.
We had recently moved her room from her nursery and switched her to my brothers room while he took hers. I've lived in this house all my life, even her room, and had never seen what was about to be a creepy experience for all of us in my household. She started making comments about how she was scared to sleep in her room because of a man in a hat that would watch her from the computer chair. She'd point and yell that he was there and would ask us to make him leave. I think he scared her so much because she was so young, but I don't know if he was ever necessarily harmful or not. I think if he was, he would've disguised himself as another young girl or boy, but I also can't be certain. To this day, she won't sleep in her room.
One of my experiences with this was being in her room with her one time when we were trying to get her more comfortable in sleeping there. She was probably three at the time, and I was laying in bed with her. All of the sudden she looked at me and started crying and said, "I can't be in here, he won't stop watching us and that's scaring me." So there I am, pretty dang freaked out as she ran out and I was just sitting there.
Now I do have a theory that maybe you guys can help me out on. After about a year of this, my mom reached out to my grandma to see what the hell was going on. Apparently, two of my ancestors (great great uncles) died in the house in that room. I never saw them when I was a kid, but my great grandma was still alive when I was that young. Maybe they're trying to connect my sister to them since they never met her? I'm not sure. Either way, it still freaks me out and I hope it's them and not something else.