Atlantic has a story on it now with a direct interview with the family. The family is in Lancaster County, PA and they are Amish. The baby was born with a midwife not in a hospital. Because they're Amish they didn't know they had created a firestorm nationally wiht people talking about it
The baby had a ruptured spleen that killed it. They were told by the midwife, before anything else, that the baby had measles and was likely killed by complications from the measles. the mother had measles herself which is how the baby got it of course.
They knew the mom had measles so they were not aware that anybody was questioning it. They're not political at all they really don't care about the politics but came forward when made aware that people, Republicans, were insisting the baby didn't die of measles. I don't subscribe to Atlantic so I can't read the whole thing but the part AI listed for me makes it clear they have no idea why the death is being questioned as not having been caused by measles as they were told by the midwife it was and apparently at some point it went to state medical folks who confirmed to them that the baby had died of complications from measles.