Suppose A, knowing he is HIV-positive, has repeated, unprotected sex with B, whom A knows to be HIV-negative, and to whom A lies about his HIV status. B becomes HIV-positive as well, as he discovers through an HIV test. Deranged with sorrow about his condition, B decides to commit suicide, and stabs himself in the chest with a kitchen knife. Just then, A enters, and is faced with a dilemma: take B to the hospital and save his life (knowing that B will be involuntarily committed to a psychiatric hospital for a while), or let B die from blood loss, even though B has never been suicidal before and has said in the past that he would rather suffer a great deal than die prematurely.
There might be different opinions as to what A should do in this situation. Either decision has problems. A is faced with choosing the lesser of two evils; but, of course, the lesser of two evils is still evil.
There is something strange about this problem, though: the rightness or wrongness of A's action now pales in comparison to the wrongness of his action in knowingly transmitting a terminal illness to B. A's actions directly and foreseeably caused the situation in which he must choose either to violate B's rights by "saving" him and having him forcibly hospitalized, or to let B die in violation of B's stated wishes. No matter what A does now, he is responsible for the harm to B, because A's action put B in the wretched situation.
This concept is what is missing from most discussion on harm to children, the proper way to raise children, and the violation of the rights of children. Knowingly creating a situation in which one will be in a moral dilemma - in which one can opt either to violate someone's rights, or allow harm to happen to that person - is itself a moral wrong. There may be debate about whether it is better to vaccinate or not vaccinate, lie to children or not lie to them (about drugs, sex, or the horrors of the world), spank or not spank, indoctrinate or not indoctrinate, allow genital cutting or not allow genital cutting, educate or not educate. But, regardless of the answers to these "lesser of two evils" questions, to the extent that the parent should have been aware of these double-binds at the time of the decision to procreate, the parent has committed a grievous wrong, and is responsible for whatever harm befalls the child.
Forcing a medical procedure on an adult is wrong. Where a child is concerned, however, it might be said that not forcing a medical procedure on a child could also be wrong - and, when this is said, it is usually grounded in an idea of a child as not having the mental capacity to determine his own values. It is my position that, where a child refuses a medical procedure that he needs to live or to be healthy, both actions are wrong - forcing the medical procedure, and allowing the child to die or to be harmed. Neither action is right. And, where only bad actions are available, knowingly getting into the bad situation should be the locus of moral responsibility for either bad action.
Related: "Fundamental coercive power is power not resting upon any consent of the person to whom it is applied." (Robert Nozick, Anarchy, State, and Utopia.)