The rationale which supports the use of family therapy when a child has a terminal illness is; The entire family is involved because what happens to one member affects them all.
It wouldn't be out of context to conclude that the entire family is involved in such a scenario as described in the task content, because what happens to one member affects them all.
Although, other reasons may seem to be the rationale for this line of action, the principal reason for the recommendation and use of family therapy in such a scenario is; because, what happens to one member affects all.
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