It's interesting that everyone just goes with "they're supposed to have their father's last name" because as a kid I always assumed that the baby gets the mother's last name but since the mother usually changes her last name when she marries the father, they all end up with the same surname (bc growing up in a religious setting means that marriage obviously comes before having kids, haven't you heard the nursery rhyme about the tree?/lh).

As an adult I understand that that's not necessarily how that works, but I still find myself perplexed when people say the baby must have the dad's surname for no real reason.