Board Thread:Questions and Answers/@comment-30980790-20170128011227/@comment-31333672-20170218110404

Sans is taller than the only monster kid in the game, and he recalls more than anyone else. He also has more idea of empathy, which means Sans pictures point of view. Many players say he jokes like he does, because Sans is depressed. I dunno how far you are into the game, however Sans is the one of the characters that remembers most of the timeline resets. I believe he can remember save/loads as well. Though a skeleton cannot grow without the normal organic structures helping it to do so, so you could say his organic form died as kid.

The shopkeeper in Snowdin does say he and Papyrus had shown up out of no where, so many connect this to him being Ness from Earthbound.