From my own experience, the best you can hope to do is to entice some sort of (universal) curiosity. Don't try to lecture too much unless it's on the grounds that your kid really wants to know how something works and he's thought abobut it. The worst you can do is try to steer to much of the mental development. Your child may never become a mathematician, and if he does, it might take a good couple of decades to develop the individuality required to go to such lengths successfully. Stay cool about it. Your son won't develop the necessary ability of abstract reasoning for many a year to come either way, so enjoy yourself and try not to think about it. He'll probably be smart enough to handle himself either way.