What limits, if any, should be placed on a parent's right to consent and/or refuse to consent to medical treatment for their child?

Abstract There is an overwhelming consensus that parent's rights to consent must be limited to decisions that are in the child's best interests, yet best interests are difficult to determine. I reflect on the case of severely developmentally delayed children, and suggest that the interests of parent and child are difficult to separate. In such cases there is a strong argument for the use of substituted judgement by a parent. Although there are coherent conceptions of the limitations of parental rights, these are based on the eventual autonomy of the child, a state that children with severe developmental delay will never achieve. Legal treatments of best interests fail to explicitly take account of such nuances, and are open to accusations of judicial subjectivity. Increased clarity could be gained by setting out the relative weight of medical, parental, and child views of best interests.