My Grandfather taught me all about the consipiracy and how our political system was being changed to promote a police state and communistic control. He always had the advice that if you are dealing with a govt worker, you should be uber-friendly and super nice, even if you are saying 'no' or asserting your rights. If you give them a reason to get angry, you'll be in a lot of pain.
In this case, i'd probably ask for a warrant but as i was doing so, i'd tell them that I needed assurance that they were from the govt and that I was concerned of thugs who might pose as 'good CPS people'. [Then tell them stories you've heard of fake cops pulling people over on the highway and how concerning it is that people would lie to the public and hurt the "good reputation" of govt workers who are trying to "help everyone"] If you're the husband talking to them, you can even "blame" your wife for being so scared of all this type of stuff and you are trying to calm her down by having evidence. Using emotion is a good way to explain your resistance and lack of trust. Good cop/bad cop routine.
If you spin it this way, and compliment the agents in the process, it sounds like you're "cooperating", even when you're not. Tell them if they get a warrant you'll be happy to let them in and then you'll have security that they are legit and you'll feel safe.
I don't know if it'll work, but it's a lot better than telling them to 'Go get a warrant' and slamming the door in their face. That's just asking for trouble.