Generally, you can prevent DFCS representatives from entering your residence. However, keep in mind that a court proceeding may be initiated (possibly by DFCS), and depending on how that were to go, you would have to allow them into your home for inspections, investigation, etc.. If any legal action has been taken re: your situation, I advise that you go ahead and speak with a family law attorney.
I agree with Mr. Rice. In the event that DFCS attempts not only just entering your home but even so much as contacts you, you need to seek an attorney to deal directly with them. It would be unwise to deal with DFCS on your own as it is very easy to talk yourself in to trouble, but very rare that you can talk yourself out of it. You want someone who will respond to DFCS who is not as emotionally and physically involved in the situation as you are so that your responses do not become evidence that the Court uses against you.
You may be within your right to refuse to allow DFCS to come to your home, but doing so would be against your best interest. If you have nothing to be concerned about, then you should speak with them. Refusing to do so may give the impression that there is something you are trying to hide, may make this more of an issue than it needs to be, and/or may make it necessary for them to take the matter to court in order to close the open complaint. Think seriously about whether there would be any benefit to refusing to allow them to come in.
I hope this information helps answer your question(s).
~ Kem Eyo
The above answer is a general explanation of legal rights and procedures. It does not constitute legal advice. Nor does it establish an attorney-client relationship between the individual posting the question and the attorney providing the answer.