I agree with the others ...if you think this child is at risk speak to the authorities ASAP
Just wondering how you have fared? Did you talk to Child Protective Services yet? I hope that you're mind has been put at ease. Please keep us informed.
Here is a reference that you might find interesting. It does say suspecting such a thing, you need to report it to the authorities. Either the police or Child Protective Services, would be my guess. Be sure your notes of what has been happening, and your evidence, is all clearly written out.
http://www.nlm.nih.gov/medlineplus/ency/article/001555.htm
If you are really concerned this is going on, talk to the police.