Im not sure what I should do....please help

I have a friend/roommate that is currently going through a divorce. There are two children involved, a five year old boy and a nine year old girl. In the past year there have been a few issues to raise my attention. 1. Last year, the five year old boy was in recurring trouble at preschool for bad behavior and was finally kicked out after a couple months after being caught exposing his penis to a little girl on the bus. He came to stay with his father (my roommate) for a few months and no abnormal behavior issues were noticed in that time, even with other kids. 2. The nine year old girl complains on weekends with her father that their mom walks around naked in from of them, hears her mom and moms boyfriend having sex, finds "moms plastic penises in the sink or laying around the house". 3. And most recently, the nine year old apparently told her friends that she "was raped and it bled a little". The friend told her parents (thank God) and the parents called child protective services. CPS made a visit and it seemed that she had made it all up....for whatever reason.
I still have strong feelings that something is going on. My roommate thinks it may be the influence of her promiscuous mom and\or promiscuous 20 year old drug addict sister. While that seems like a likely contributing factor, I am not entirely convinced that is it. I'm not sure what I should do. I am worried about these kids. Something is telling me there is something wrong. Should I report it? Is what I know grounds enough to report it? I just don't know what I should do....please help.