Sounds to me like the reporting to CAS is actually aimed at the OP/Daycare provider. Even though it was their child who caused harm to another, I get the idea that they are going to try and push this in the direction of how you neglected to take close enough care of the child causing this incident to happen....from what you have told that they said, that is the impression I'm getting.

I do think this is all kinds of ridiculous and would hope that it's either just an empty threat and hot air coming out of this mothers mouth, or that the CAS workers supervisor won't follow up because there are no grounds. Sounds like a whole heap of mess to me. Bloody police officer, assault my ass!