Speaking as a former police officer...in many states, when a law enforcement official goes to your home for a situation like that (ie something that could possible be a domestic/partner family member abuse situation--I know it wasn't but that's how it would appear to them), they are required to report it to CPS. As for the temporary restraining order, I don't know why it wouldn't have simply expired without you doing anything, unless it was made permanent. An example of a situation where it would have been made permanent is if the petitioner (you?) showed up at the court hearing and the respondant (your husband?) failed to show up to contest it...although you should know if that happened.
The chances are that if you allow her to see if the baby and he's obviously fine, the investigation will be dropped. HOWEVER, for your protection, it would be best if you at least have an independent party (like a pediatrician) examine him to document that's he's not injured in any way before you let her see him. And you do not have to let her see your baby unless she has a court order. In my state, a court order would probably specify that CPS is allowed to make contact with and examine your child. Law enforcement could assist them to make sure you complied (basically keeping the peace). You could simply step outside, or possibly arrange to meet them somewhere, you wouldn't have to allow them into your house without a warrant (different from the court order). But if they have a court order to see him and you refuse to allow that the next step would be for them to get a warrant to enter your house. That is how it would likely work in my state, but things may be different where you live.