Visitation rights of a convicted child abuser.

My friend has a daughter. She met a man a while back and had a son with him. During their time together he sexually abused her daughter who was around 6 and 7 at the time. He did this while his son was around. I do not know all the details, but I have heard that he would lock his son in a closet while abusing her daughter. This man was eventually found out and ran away. After a year he was captured and jailed for about 5 years. He is now realeased from jail and has a probation order that he can not be around children. He just took my friend to court to get visition rights to see his son. My friend can not believe that the court would allow this, however they told her that his rights as a father come before the probation order and are setting something up , I think it is some type of supervised visits and her son will have to go to therapy of some kind. My question is, Due to the fact that this man sexually abused one child and mentally abused his son is there any way for my frined to prevent the visitation. Her son is now ten and her daughter is 14 and both suffer from emotional issues and see doctors for these issues. This just seems like it will cause more stress on her daughter and my friend as well. Not to mention what it will do too her son. He knows what happened and has expressed his confusion and anger at the issue.
Any advice would be very helpful.
Thank you