There's young children in danger and you're here and with a very vague post so no one can even give you the correct advice???
What are they in danger from? A paedophile? Someone who may murder them? A kidnapper?
My first port of call would be the police, this call would be logged and then the police could run a background check, organise a raid etc..
Those saying call social services, haven't any of you seen the news? Instances not logged, paperwork lost, the police not being called when they needed to be and there are too many examples but let me draw your attention to the sham which was the Baby p case.
Hc4361, i implore and beg you to inform the police asap for these kids safety as if any harm ever comes to them you may have to live with the result of your actions or indeed inactions for the rest of your life.