When DS was 2.5 he had two friends, Jim and Jack, who had blue faces. Jack always crashed the car so Jim drove. They often knocked on the door, and I had to shake hands with them. Woe betide me if I picked the wrong height to shake at. Over time, they acquired a mummy, Julia, who abandoned them for weeks just after DD was born. DS was cross with me of course, and Julia returned the day before he told me he loved me again. They also had a little brother called Ozlin Chair Sozlin. They were builders and he did work for them for £7 a day.
In the end, quite brilliantly, they ripped him off on a major building project and when they spent all the money they owed him on beer and betting on horses (my dad's hobbies emerging here) he ditched them. grin
I kind of miss them. When I asked after them the other day he looked vaguely embarassed. About 10 minutes ago I described DS, now nearly six, as fabulously nuts on another thread because according to him there were 64 lions in the playroom at one point today. He dictates really brilliant stories that we make into books. His imagination is wonderful. Julia gave me a fantastic invisible recipe book which helped to broaden his taste in foods.
I'd say sit back and enjoy it, and make use of the friend when you can, but I know that not everyone is comfortable with how far this can go. A deeply practical friend of mine just couldn't cope with Jim and Jack at all ... Any mention of them had to be banned when she was about.
The funniest thing I ever heard on the radio was an hour-long phone-in on Radio Five about imaginary friends, many of whom met spectacular deaths.