We make the mistake of thinking that people who believe in “faith healing,” “psychic surgery,” and all that other foolishness will change their minds once their children start dying. They won’t. That’s the “faith” part of the equation.
To such a person, that death is exactly what was supposed to happen. It’s not that they don’t care about their children. They do. They simply don’t (or won’t out of peer pressure, but that’s outside the scope of this) see at all the connection between the actions they have taken and the death. Cause and effect is reversed when it comes to the exertion of faith. The death was always going to happen — the only difference to them was if they danced the proper dance. If they did, the gods are happy, and if they didn’t, the gods are sad (or worse, mad. Either way, there is some sort of punishment).
Trying to circumvent such “faith” in order to protect a life is an act that is counter to their belief. This is a misunderstanding of the most profound nature of faith. Asking such folks to not believe their magic can cure a child is essentially asking them to not believe in their magic.
Note that this is not a call to prioritize such “faith” over actual human lives and suffering, just a reminder that when fighting such forces of evil, it’s worth remembering that they truly honestly believe that they are doing the right and righteous thing.
(addendum: It is sometimes the case that people can change their minds. In either direction. Sometimes all it takes is a catalyst. Again, distressingly, in either direction.)