It's not really relevant for most vaccines, because they are usually given way earlier than a child could reasonably give informed consent, but yeah, kids here do have the ability to make some life choices about their medical care that kids in the US don't.
HPV vaccine for adolescents aged 12 to 13 years old | nidirect
The key part:
It is important to note that if your child is between 12 and 16 years of age, the final decision to have the vaccine is legally your child’s as long as he or she understands the issues in giving consent.
Social services wouldn't need to be involved, just the child and their doctor or nurse.
The same applies to some other medical choices when the child is over 12, roughly (it varies), so for meningitis, for example, I think a child could get a vaccine withou
It is a very American idea, you're right. I'm sure it exists elsewhere but it's really strong there.