When discussing the issues of recording conversations with authorities from Child Protective Services, there's much debate on whether to inform the other party that you are recording. While I understand both sides of the debates, I heavily favor notifying the other party, even if you are not legally required to do so, unless they have already committed a violation and secret recordings may help you prove it.
If we're dealing with an initial CPS contact, though, I would say record, make sure they know you're recording, remind them several times throughout the conversation. Although they may want to do so, they cannot deny you your right to record the conversation (it must be noted that they have an equal right, and, in my experience, when you pull out your tape recorder, they pull out theirs, and suddenly, the recording they are doing is no longer secret).
As Dan has rightly pointed out, our first objective in dealing with CPS MUST be the children. Keeping them home and safe is our first priority. When they know you are recording, CPS is more likely to act in a Constitutional manner, and respect your assertion of your Constitutional rights, because you have a pretty solid piece of evidence against them if they do not, and CPS does NOT like litigation. They are less likely to remove a child, because they must prove to a court WHY they removed the child, and a taped record of the conversation can raise reasonable doubt on their assertions. Just like asserting your rights BEFORE the investigation begins, while they may not like you, they will be forced to recognize the legal limitations of their investigation.
There may be cases where violations have already occured and where secret tapings may help prove this has happened. In those cases, secret tapings may be advisable, if they are legal in your state, but I personally believe that in most cases, letting CPS know EXACTLY what you are up to is the best protection you can get. After all, "the best defense is a good offense".