LOL! Well, in a world where stenrects exist, mysteriously appearing strangers and pygma banthas might not be such a big deal.
The baby is little Prince Brion, born after 1130, so that's why there's no mention of him in the Codex. I figure Kelson and Araxie wouldn't have stopped making babies just because the Codex decided to stop recording history two years after their wedding.
Prince Brion got a mention (of sorts) at the end of Visionaries
, as the baby Araxie was pregnant with at the time AEdwige's sentencing and execution took place. (The reason Kelson was a bit green around the gills hearing from the midwife about the labor complications that AEdwige was going through in giving birth to her late husband's heir, because Araxie was also pregnant at that time and he didn't particularly need the powerful reminder of the dangers of childbirth!)
No, wait, sorry...it just occurred to me that Araxie was also expecting a baby at the end of The Killing Season
(remember, Kelson panicked when Araxie got sick in the morning because he thought she'd caught the fever-flux, but it turned out she was just pregnant again), but that child would be toddler-age by this point,so maybe either that's Prince Brion and is at home with the nurse for some reason, or maybe Araxie and Kelson lost a child between Javan and this baby. It happened all too frequently back in those days, even with the best medical care available.