In fact, I see a solution

I can’t conceive of any context in which this doesn’t mean “the suffering of children is a good outcome.” Like, the suffering of children will convince their parents that they were wrong?

There is a simple solution:

1. Vaccinations are provided at no cost.
2. Vaccinations are required by law. No religious exemption. No “I’m a parent and I say so” exemption.
3. Day one of school will be vaccination catch-up day for kids who have fallen behind.

That won’t get everyone. But it’ll get enough to ensure broad community immunity. The people writing and implementing the laws just have to be willing to grow a spine and say “your opinion as a parent does not overrule medical science.”

That used to be a thing in a lot of states - admittedly, there were some more exceptions, but generally school districts were reasonably strict about it, as a matter of public and community health. But the antivax movement took a lot of the teeth out of those mandates - so much so that many places in the US have lost their herd immunity as a result of so many idiot parents “doing their own research”.

Simple, you don't convince them. You give them no choice and impose penalties for not doing it.

Good thing they aren't the final arbiter of truth, the all knowing, omniscient, all powerful enforcer of that which is true and just. But you aren't either, so its good that you also don't have that power.