Another bro or sis?

He's a child, around 3 - 4 years old, but he talked like an adult. He said he was my bro (or sis? I dun't remember, i think it's bro) . He said that I might not know about him. But he said he just came by to visit me since he thought I have done something that disagree him and he wanted to critisize me ( I don't remember what it is). I felt angry and ignore him, but his eyes I cannot forget.