I'm not entirely sure contracting and entirely preventable disease is as act of God though is it
Of course it is. There are plenty of unvaccinated people who do not go on to contract the disease in question, the only difference between those and the people who do is happenstance.
That's like saying folk that died of cholera or bubonic plague died due to an act of God
Precisely, because they were the unfortunate ones, unlike the other people living in the precise same circumstances at the same time, who didn't contract cholera or plague through sheer good fortune. You can't have it one way and not the other.
At the very least, it has to be child abuse
Well no, because as things stand it is not illegal to opt not to vaccinate children. It might be morally questionable, but while it's still perfectly legal I don't think it's in any way reasonable to term it "child abuse".
I mean Christ, you take your child out of school for five days and your getting a fine
That'll be because the State legally compels you to educate your children, so by withdrawing them from education without reasonable grounds you are in breach of this legal obligation. You are comparing apples and oranges, because again, it is not a legal obligation to vaccinate your child.
Barring a health condition or a legitimate reason not to vaccinated there's absolutely no reason at all children shouldn't be protected. "Mummy thinks you might get Autism, or get a little poorly" or any other crap is not an excuse or a reason not to vaccinate
Then the law needs to be changed to compel this, and by doing so you would also open the way for people who refuse to be prosecuted without the nonsense of the original suggestion, which amounted to "we are going to prosecute you retroactively for doing something which is and was perfectly legal"
The law does not prosecute people because they made morally dubious but perfectly legal choices, it prosecutes people who have acted illegally and broken the law. Although I think there would be issues regarding personal liberty if you compelled people to vaccinate, the State does legally compel Guardians to educate children to a certain minimum standard, so it's not as if there aren't already precedents for the State taking choice out of parents and Guardians hands and mandating that all children have to be subject to a certain stricture.