I firmly believe we are all born with imagination, and that it is gradually stamped out of us ( often by school, which ought to know better). Are the imaginary friends beloved of small children any less real to them than 'real' people? Does a child with a doll see an artifice, or a baby? I know my dolls were pretty real to me, and I remember repeatedly explaining to them how it happened that only one of them was black, even though they were all my babies ( too complicated to go into here).
My youngest son, Joe, had a tribe of imaginary friends, and got furious if, for example, we shut the door and left one outside. Sometimes, he actually became one of them, the favourite being Bob. One afternoon we had this surreal conversation ( he can't have been more than three at the time, if that):
Me: Come on, Joe. Time for your rest.
Joe I'm not Joe. I'm Bob.
Me: Okay. Come on, Bob. Time for your rest.
Joe/Bob: I'm not sleeping in Joe's bed!
But life soon puts paid to this kind of thing. Just as well, really, since I would just have had Joe, Bob and his/ their girlfriend staying over Easter. Which might have been complicated.