Do you think a 12 year old is mature enough to understand all of this without any education or information, which you would assume is the case from your bad parent examples. Are they being advised at time of vaccination? Or is it more likely that they are getting hey, its all good and we will give you a $20 PNS voucher?
They should remove the voucher incentive for kids. Most kids understand the fundamentals of infection and disease, they are schooled in using soaps and covering their mouths, good nose blowing technique from a very young age.
We are living in a time where kids aged twelve are highly aware of the global pandemic, the mask wearing by everyone in public, why that is, the existence of the disease and the risks it posses. Most kids know the fundamental purpose of vaccines by this age. They understand why they cannot go to school and so on.
Informed consent can be done well for younger people with skilled communication and the right approach.