Blood transfusions signal to me something potentially life threatening. Which is really the only scenario I can think of that overrules parental consent for medical procedures in general (at least in Oz, as far as I’m aware.)
On a personal level I’d think this is, well wholly dumb and idiotic, to be frank.
Not only is it just paranoid, it goes against decades worth of medical science that we can verify and see for ourselves.
(Your blood isn’t actually altered by vaccines! I learnt that in freaking primary school. Jesus this stuff is beyond basic! So what difference does it make???)
On top of that blood that’s donated is already is short supply since it’s totally voluntary. And on top of that, blood may be rejected due to the strict screening process that’s been in place for decades (due to things like Mad Cow disease.)
So I mean you have to take what you can get, is what I say lol
However, unless it’s a life threatening situation, the parents can refuse if they so choose. I mean JWs famously deny blood transfusions. For themselves and their children and outside of life threatening scenarios(for the kids) that’s their right to do so here
Again, as far as I’m aware.