Realistically, the FBI cannot reduce or suspend your sentence. The best they could do is tell the court that you were cooperative or "lose" some of the evidence so that you would have fewer charges. I suppose they could explain that you helped catch a child abuser, but it is ultimately up to the court on whether or not you get a lighter or suspended sentence.

To answer your question, my idea of abuse and their idea of abuse is totally different. It could be that they just want to nab a true pedophile who is in a totally consentual, loving relationship with a child. Even if they told me that he was really abusing her, I wouldn't trust them enough to believe it. They would say anything just to make a bust.

I wouldn't do it. It is their job, let them do it.