To sterilize a bottle you simply need boiling water without a significant amount of toxic materials in it. To get boiling water you need water, a container for the water, a combustible fuel, an ignition source, and a means of transferring heat from the burning fuel to the water. Even if you don't have a metal pot you can do stuff like heating rocks and then stacking them on cool rocks inside a plastic, glass, ceramic, wood, etc container filled with water to get to a boil.

Sterile bottles? Millions of babies around the world are doing just fine every day without that.

Some parents of infants would be able to find a way to feed their children safely.

You mean everyone who didn't have an issue because modern hospitals have backup generators that can run for days, or even indefinitely if diesel-based?