As somebody who lived in an abusive situation (not my parents, but the woman they hired to take care of us), I thank you. If I were those two kids, I wouldn't give a rats' ass about what your motivation was when you called the dad/CPS. I would be so happy that an adult acknowledged that I was living in a unstable situation and had the strength to do something about it. All the neighbors heard our caretaker scream up and down the block and they did NOTHING. Nobody told my parents, and my caretaker was smart enough not to leave marks. She just used needles instead when emotional abuse wasn't enough for her.
I realize that I'm also projecting because my sister prefers to live/screw her pothead boyfriend and live in fantasy land rather than feed her two children, so my parents, her ex-husband, and my husband and I are left holding the cards. I realize that my sister acts this way because of the abuse she faced as a kid (not just from our caretaker but from others who saw her vulnerability), but I also realize that recognizing her pain doesn't mean that I turn a blind eye when it comes to HER children.
So yes call CPS.