I want my future kids to not believe in mythical stories
Why do you not want your kids to believe in myths?
It's all untrue nonsense and all I ever hear. Can't they come up with better things to discuss among each other?
I think it's good to free your children from unrealistic fantasies once they reach a certain age.  Grounding them in a realistic outlook on life sets them up for future success!
It would be good for them to be more realistic.
Children like to daydream so try not to push them too fast to grow up. Try to find some examples throughout history of something fantastic occurring and showcase how reality can be just as interesting.