That is not what the assisted suicide debate is about. The debate is about the right to kill someone who cannot do so themselves.
«On February 13, 2014, Belgium legalized euthanasia by lethal injection for children,» from [1].
«Even the controversial head of Belgium’s euthanasia commission is concerned that a well-known Belgian psychiatrist is allowing too many of her psychiatric patients to be euthananised,» from [2].
1: http://www.patientsrightscouncil.org/site/belgium/
2: https://www.bioedge.org/mobile/view/belgium-euthanasia-docto...
https://www.bbc.com/news/world-europe-26181615
Perhaps the law is not being applied this way, but I think the idea here is "this poor child is in agony with no hope of improvement and keeping them alive is torture in a sense" - not "let's take terminally ill children lightly"