Not gonna ramble on too much more, but I'll just say this: pretty soon, Oda's gonna reveal that Big Mom wasn't the only...polyamorous pirate running around. These freedom-loving figures had some very liberating, open attitudes as it pertains to relationships. Not for nothing, many seem to associate Roger w/ real life pirate Calico Jack Rackham, and I think many are already familiar with the rumors surrounding his love triangle with Mary Read and Ann Bonny...
As for Roger possibly having left another lovechild in this world, I doubt he would've known of his/their existence(s). Won't blather on too much there either, but I will say that Roger's words were sorta prophetic, even if it may not play out as he anticipated; a son of his will be the one to walk out of Laugh Tale as Pirate King. Heehehehehe.