The Dutch health law says children and parents decide together in the age group of 12 to 16. The law also states that if the child and parents disagree on health care matters, doctors will follow the child. This is not an opinion. This is what the health law says.
I must also add that in practice, this hardly ever occurs because in most cases that I know of, especially in end-of-life situations and palliative care, parents and children think alike and decide alike. There have been cases in the past where, for instance, one parent would not allow withdrawal of treatments or intensification of treatments, the child wanted the contrary and a second parent was somewhere in between. Those things sometimes happen, and we would follow the child.