Hey L.,
I agree with all these other moms,
Something needs to be done.
My oldest child is 13, I just started letting him go out alone.
In CT I think your supposed to be 12 to be left alone, tho I know many parents do it earlier.
I would tell your friend not to call the police, But to definately talk to her ex, if he doesn't listen, haul his butt into court and have them send him to parent classes before he can get his visitation back.
This way he knows she is serous. BUT NOT trying to ruin his life. or the relationship with his kids.
Any judge would understand her concern.
And I honestly don't think that having him arrested, will help make things better. Plus if he can't get a job how will that make things better for her kids.
NO the best option is to make him get the training her needs to be a better father, She could also agree to take them aswell, It never hurts to be reminded of the right way to parent.
M