I think an assent approach would be more useful. It's really about the conversation, the nature of the relationship with the family and recognizing that, if this child is very ill and will die, the family is going to carry on afterwards. You would rather have a family that can carry on together, as a unified whole, than a family that is fractured into pieces and never speaks to each other again.
That can be the role of the team involved in doing the assessments and providing that level of support.