if you have information that would help the case it is your duty to report that to the police. relationships be damned. it is a child's life you are talking about. forget the adults, they are not the real issue. the safety of a minor is. the claims must be believable enough for the other person to be detained.

if you have doubts, then go to the police. if she if falsifying the claims to the point the other party has been detained then that is severe as well. causing false imprisonment, especially on sex abuse charges is very dangerous.

as I said, the cause of concern is the safety of the minor. let the police deal with the mother to see if she is fabricating claims against the father (or who ever it is) . that is a sure way to unwind everything and make sure that in the long run the child is safe, no one is falsely imprisoned and perhaps she gets at least recognized for needing treatment.

to do nothing because you want the child to remain with the mother and leave the man detained, while you know there might be a false claim puts YOU at risk for police charges since you were aware of the issue. plus, just how could you live with yourself for allowing a perhaps innocent man to be detained and do nothing about it????? seriously.