HelloCustomerand welcome to JustAnswer.
Your question suggests that you have some familiarity with munchausen syndrome by proxy, which is a variation of munchausen syndrome
People who suffer from munchausen syndrome typically suffer from an abnormal need for attention which is exhibited by pretending to be sick or actually getting sick or injured on purpose.
Munchausen syndrome by proxy (MSBP) differs in that the person involved tries to gain the desired attention by injuring or making some other person ill. Unfortunately, the most common form of this disorder is when a parent causes illness or injury to a child.
The Mayo Clinic website has an excellent discussion of munchausen's, written in non-technical terms. You can see it here:http://www.mayoclinic.com/health/munchausen-syndrome/DS00965
From this introductory page, click on the link "Symptoms" and then following links to review the entire discussion.
Regarding proof, note the Mayo Clinic observation: "Although it has been recognized for centuries, Munchausen syndrome remains mysterious and difficult to treat." They could have added to that "and difficult to prove".
For an FBI bulletin on MSBP which discusses the investigative and evidentiary difficulties involved in MSBP prosecutions. You can see this five part article here:http://findarticles.com/p/articles/mi_m2194/is_8_72/ai_107930064/?tag=content;col1
Additional information about MSBP is also available at these sites:http://www.scribd.com/doc/90980/Munchausens-Syndrome-by-Proxyhttp://www.aifs.gov.au/nch/pubs/issues/issues23/issues23.pdf
Needless to say, if you suspect that a child is being injured by someone suffering from MSBP, you should give serious consideration to reporting the situation to authorities who are trained in recognizing and dealing with the syndrome. You might very well save the life of the child; or at the very least, prevent the infliction of significant physical and psychological harm.
Thanks for asking your question here on JustAnswer. If you have any other questions, please let me know.