She told me it was dangerous for a baby's head to be unprotected.
Do you think maybe that was just an assumption long ago and not today?
But people didn't know about it. They didn't have any science at all, and babies died often.
I can see why this might be upsetting for you. It's good to warn people if something they are doing is dangerous. You can always consult your doctor if you think something might be wrong.
It gave me a headache to learn all of that stuff.
I am sorry that it gave you a headache, it is a lot to learn about children when you have one. It is good to warn others if you have new information about childcare. It will help them from doing something that could be dangerous to a child.