I agree that it is a stand in for a name. Some ideas on why that might be: -- sometimes babies don't immediately have names, and we need a way to refer to them

I agree that it is a stand in for a name. Some ideas on why that might be: -- sometimes babies don't immediately have names, and we need a way to refer to them -- professionals who work around babies and in birthing tend to address both the baby and the adults by their family relationships (it's Mom, Dad, Grandad, etc. instead of George and Laura). This is presumably because that helps it keep clear what everyone's the relationships is to the baby, and what role they should play in the whole process. -- babies aren't really people with their own unique identities when they are first born, so maybe it is kind of awkward to address them with their full adult name.