When my younger brother was around 4, he had an imaginary friend named Victoria Meadowbrooke. He told us that she was the prettiest girl ever and she floated above his bed a night.
When my older daughter was two or three, she used to have a couple of imaginary friends, Dodo and DeeDee. They were typical imaginary friends. She would talk to them and play with them, and tell me about their lives.
Then one day, when she was about three, she was talking on her play phone when I walked into the room. She “hung up” her phone and said to me (with a completely flat voice and deadpan expression): “The Evil is coming.”