I firmly believe that my gut feeling is the only thing to listen to in these types of situations, as Zoe says. To me, THAT is my HP talking to me.
For what it's worth, I think he should show you in others ways that he is trustworthy enough to look after the kids. It seems dangerous to allow him to do this before he has proven himself in other ways i.e. demonstrated efforts at recovery.
You know what to do - listen to your own voice.
Love
Minnie
xxx