Question about sexual abuse; what should I do?

My cousin contacted me today through Facebook. She told me that a person on my friend’s list was the same guy that molested her niece along with many other kids in their neighbourhood years ago. Turns out that this guy is my ex girlfriend’s (who I was with for 10 years) brother. He is now 31, married and has two kids. The abuse happened when he was a teenager and was babysitting other young kids.

I remember when my ex and I were together, she had mentioned something about her brother ‘getting in trouble for doing something to a young child while babysitting’. And, really, that’s all that I remember her saying. When I talked to my cousin today, she said that “he got away with it because he was a young offender, but was ordered to go to counseling”. Now, here she is coming to me all worried about his kids, thinking that he may have done or is doing something to them. She is really upset by all of this. Apparently, he did some pretty awful things to the girls that he had babysat. I get the feeling that she wants to me approach my ex and talk to her about it. I wouldn’t even know what to say, if I were to talk to her about it. What should I do?