This appears to be somewhat of a legal question, but this would not recategorized to legal.
So I will answer from a medial perspective and based on my experience over the years with MS and MSP [Munchausen's syndrome and by proxy].
The person you suspect of MSP would have to be diagnosed. The best way is if they seek help.
If the child was seen for medical problems that the doctor determined, or determines were induced by an adult, then MSP becomes a clear possibility and it is then a matter of proving who the perpetrator was, which is based on evidence collection and the legal process through the legal system.
The next step here would be to call the authorities after having the child talk to the doctor and to a child psychologist if needed, to see what happened.
As far as consequences to the perpetrator, these have a wide range, which can go from negligence to abuse and worse. On the other hand, the person with MSP is ill, so in many cases treatment is dictated.
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