In my area, CPS has been known to bungle many reports of abuse. In fact, a number of years ago they were in the news here because the negligence of the CPS led to the death of a couple of children. The family was reported to CPS a number of times, but in the end CPS kept returning the children to the family.
I had some issues with CPS when I was a kid. I was in a foster home when I was 14 because my biological mother was abusive, was dealing and doing hard drugs, and was not feeding us.
My brother and I called CPS. We wanted help. The guy on the phone thought we were lying. He said we "need to communicate with our mother better". He thought we were just being liars. I ran away and, after a number of events, was placed in a decent foster home. When I had my first court hearing to be placed with that particular family, I had told the judge about the phone calls made to CPS.
Recently, CPS in our state started making some huge changes. Since the deaths of those kids, CPS is taking more care in attending to reports of abuse. However, they are still lacking.