As it is family I would investigate as soon as possible yourself and if your concerns grow stronger please do not hesitate to notify authorities. I read some great advice by Bruciegee you should have a look at in the advice section. Hope it goes well for you and the kids

I wrote an advise on the topic of what to report and what not to report to child protection services  a little while ago. If you click on my name, my page will come up. If you click on the word advice in the box on the left, all the advice I've written will come up. it was the first one I wrote that would be the most help to you.

As I've written that, I won't go into alot here. But I will say that it's not your responcibility to determine if it is true or legitimate. Leave that to those that investigate these things everyday. You can actually end up messing it up to the point where they can't do anything, if you try to look into it yourself. We are specially trained in how to handle these in ways that stand up in court...

Please read the article i wrote, and either call or not call based on what you know, without trying to dig up more info. be natural, and you can always call later if you get more information. But please document what you do know, and don't hesitate to call if you are worried about their safety.

It appears that you're getting this information second hand, so you should pop around a few times after work unannounced to see if it is legitimate.