I do think it’s worth noting that Toriel’s arguably had more than two kids (three counting Frisk, though it’s possible to leave instead of staying with her, and nine counting all of the fallen humans) but…
tbh i kind of really hope sans and toriel have the same kind of online friendship as terezi and dave
like 3am “Hello Sans! I just wanted to know if the attached image file in this message is a true picture of you or not?” and shes sent him a fucking picture of a skeleton from google but drew on a shitty hoodie and eyes in
mspaint
and hes always like “damn toriel how are you getting these amazing candid shots of me” and sends back an amazingly shitty picture hand drawn with the mouse on mspaint of a goat screaming as it drowns in a sea of stock image pies from google at various overlapping heavily jpeg compressed sizes like “this u?”
Yeah, all that angsty stuff where he remembers every timeline is…well, inaccurate. Non-True Resets seem to leave echoes among everyone who’s met Frisk, but Sans’ knowledge of timelines means he can take these echoes at more than face value. And he’s incredibly perceptive and can even usually get the count of how many times you’ve died based off of your expression, although at the higher counts he starts getting it wrong and gives up.
It’s interesting to note that another character, who actually has no knowledge of resets or anomalies to work off of, can do this to an extent.
She sees Frisk’s facial expression after they’ve killed her and reset, and zaps them on the spot.
It’s worth noting that people who are able to accurately read others’ facial expressions (particularly with the pinpoint accuracy these two do) often are highly empathetic individuals.