My oldest did not go for the idea of Santa and soon started writing letters to the tooth fairy, "Dear Toothfairy (Mom) please can I keep my tooth." It was difficult as a mom with other parents whose kids were all into it. My kiddo has always been the logical one. She would state all the reasons why there could not be a Santa. Parents were mean about it and expected my youngster to be silent. I did not. I am not sure how you bridge that gap but logical kids have the right to their opinion. She had quite the slew of imaginary friends, but never believed them to be real. I also do not equate the belief or non-belief in Santa or the toothfairy with the scope of imagination. I do subscribe to honesty with my kid and securing her trust that I answer her questions honestly. As far as I can tell it has paid off for the big questions of middle school, which I still answer honestly. She brings them to me. Those are life and death kind of answers that she needs the correct information, not what her peers tell her, and they tell her some pretty off the wall incorrect stuff!
