Final answer:
Doctors can override the wishes of a child under 18 in urgent or life-threatening situations where immediate treatment is necessary, even without the child's or the parents' consent, according to the 'parens patriae' doctrine.
Step-by-step explanation:
In certain situations, doctors can override the wishes of a child under 18 when providing medical care. Generally, parents have the legal authority to give consent on behalf of their minor children, since children are not deemed legally competent to make their own health care decisions. However, there are exceptions to this rule, particularly in urgent or life-threatening situations, where a physician might determine that immediate treatment is necessary to preserve the child's health or life, regardless of the child's or parents' consent. This principle, known as the 'doctrine of parens patriae,' allows the state to protect those who cannot protect themselves.