What is in the best interests of a child, and could that ever include interventions that we might regard as prima facie detrimental to a child’s physical well-being? This question is raised a fortiori by growth attenuation treatments in children with severe neurological disorders causing extreme developmental delay. I argue that two principles that provide guidance in generating a conception of best interests for each individual child yield the right results in such cases. The principles are as follows: the potentiality principle, whereby every child should be able to develop its potential and is entitled to receive certain help in doing so, and the principle of psychosomatic harmony, whereby every human being is entitled to treatment that is appropriate to or enables a life in which mind and body are in tune with each other. These principles indicate a certain response to what we can call Ashley-type cases and admit certain caveats.