Help! What should I do?

Yesterday, I found out a convicted pedophile has been hanging out with kids of family friends. Now I find myself with this awful dilemma. Do I tell them?
 
It sounds so simple when written in that one sentence. But it’s so much more complex than that.

You  know this strange beast called Facebook? Weird things can happen. Like yesterday, I peruse my newsfeed, I see a friend’s post, I read it. Then, I see a name! A person tagged by my friend. What’s if it’s the same person?! I click on the tagged person, and I see. It’s him. The pedophile. But wait. On his profile, I see the son of another family friend, the two of them, hanging together. My mind screams, “What are you doing with him!? Do you know?”
 
So I call my own family member who was more involved with the situation when it all blew up the first time, who was close to the family of the original victims. It’s confirmed. Same person. He was convicted, but copped a plea; got off without prison time. Moved away for a while. But his victims, they couldn’t get away from it. Ever.
 
My own children hear me on the phone, and when I tell my husband about it, asking, “What should I do?,” my kids say, “Wait, Mom, we know them. We went to school with them.” They've seen that person, his posts, those friendships.
 
I think of the kids of my friends. They clearly (via Facebook) have an ongoing, in-person (as in off of Facebook) relationship. Who am I to cause strife there? Who am I to pass judgment, to share information? What about grace, forgiveness, rehabilitation?
 
What about statistics? Recidivism? Inability to reform, or refusal to get help? What about innocence lost, the victims, the children???
 
I can discretely meet with my friends, the parents, and I can say, “Do you know? Is everything okay?” Or I can say to myself, “That’s none of my business. Who am I?” The cost may be high. I might offend them greatly. I might scare them. I might ruin that friendship. I might ruin their friendship with that person. I might be totally out of my mind to even consider meddling. 
 
I might let something continue that shouldn’t because it is none of my business.
 
I don’t know. I’m seeking wisdom. I’m praying and meditating, asking "What should I do? "