It sounds like the child may be a sexual offender but without directing evaluating the child it is hard to say because there are many other factors, such as bed wetting and lack of empathy that are looked at when deciding if a child is reacting or acting on their own.
The fact that there is a suspected history of sexual abuse may be confirmed by how the child is acting out right now. Children do not suddenly develop sexual deviant behavior, they usually learn it from somewhere. It sounds like this child may have been abused.
A child that has been exposed to sexual behavior will react by acting out what they have been exposed to. So if the child saw someone being sexually inappropriate with animals, even on TV, the child may act that out. If they were exposed to others having sex, they may act that out as well. That would be considered reactive sexual behavior.
But if the child was abused or exposed to others being abused, they may become sexual offenders themselves. How you tell is when they child has intention to hurt or is consciously aware that they want to hurt another person by sexually assaulting them. You will see a lack of empathy and a disregard for social rules and norms.
I highly recommend this child be evaluated by a trained therapist who has experience in dealing with childhood abuse and sexual offender behavior. You can find a therapist by searching on line at http://therapists.psychologytoday.com/rms/.
Let me know if I can help any further,