It's a simple answer. Carter doesn't limit to terminal illness, to a terminal phase of a terminal illness. So those are cases, with respect to withdrawal of nutrition and hydration, in a child who is terminally ill. It's simple. Carter is not just about terminal illness.
Evidence of meeting #11 for Physician-Assisted Dying in the 42nd Parliament, 1st Session. (The original version is on Parliament’s site, as are the minutes.) The winning word was illness.
A video is available from Parliament.