Imaginary Friend

Thomas has an imaginary friend named Russ.  I don't really know how to handle this, nobody in my family has ever had imaginary friends.  Michael and I just kind of played along when he started doing this and thought it was funny but Thomas talks about Russ and to Russ more and more.  Finally, the other day Thomas started talking about him again.  I said, "Thomas, you know that Russ isn't real, right?"  He said, "oh yes, yes, Russ isn't real Mom."  Then he turns to the wall and says, "Russ, you not real, you not real Russ, ok?"