Hi, Worried aunt, welcome to PsychCentral (PC).

What a wonderful aunt you are to be concerned. I don't know that one can know how someone is going to feel and/or act in the future. There isn't really any such diagnosis as "nervous breakdown" that is just like saying someone has "cold or flu" which can be one of many illnesses.

I do not think the family member will be worse when they leave the hospital, I would wait and see to what extent they wish to see the child and how adults feel being with them. Unless you believe they have harmed the child before, there should not be any reason why they would start now and if, when they are out of the hospital they are not drugged so their ability to care for the child is compromised, there really should not be a problem?

See how you feel interacting with the person; it is possible that the child is not going to be the first thing on their mind, what with having been ill and away for treatment? I would suspect the custodial parent could talk to the person's doctors and express any concerns?