Thanks everyone for your thoughts, its really good reading different viewpoints and opinions.
I talked with Sarah - she is devastated and feels like she has to choose between 2 people she loves. But she wants to give him a chance and is hoping the am classes and upcoming parenting course will help him. We talked about letting CYFs know of our concerns and that they would likely help them in their parenting. But she is really struggling with 'getting him in trouble' and 'being in the CYFs system' as she believes he wont do it again and is working toward being a better Dad.
I really think that their 4 month old needs to be protected tho. She can't protect herself. So I'm gonna hold off for now, but keep a close eye on them. And Sarah knows I'll be 'spying' and is happy with that. She agreed that if anything happens again we'll let someone know.
What a tough situation. Argh.