She can (and perhaps should) go to a shelter, and take the kids. The shelter will have resources available to her to help her file for divorce and get temporary custody orders.
I realize that you're worried about your friend. But you don't live there 24/7, and you're only getting one side of the story. The kids ARE being fed, housed and clothed - hence CPS is likely not going to do anything. If the kid are genuinely being starved - and I mean starved, not just "not getting what I want to eat tonight" - then of course CPS needs to be involved.

