If Sailor Moon was written after Naoko was married and had children, I feel like Usagi and Mamoru would have definitely had a son... Considering that Usagi is meant to be Naoko's author avatar in some respects.
It would change the dynamics of the manga's story though, since I don't think Usagi would be quite as jealous of Chibi Mamo the way she was with Chibi Usa. In fact, it might completely turn the story over its head.
His name would be Mamoru LP (Little Prince) Endymion, but everyone would call him 'Chibi Chiba' instead. Instead of a pegasus, the Dream arc would probably have had a fairy, mermaid, or sphinx for him to semi-fall in love with. Instead of a Sailor Soldier, he'd transform into Tuxedo Little.