CP parent is Custodial Parent. However, this is does not mean in all cases that a CP has sole custody. It depends. It is just a title and is often used in child support cases to distinguish between the obligor and obligee. Obligor being the one who pays support and obligee being the one who recieves the support. Or, just used to distinguish between which parent the child lives with. Some people think titles like this shouldn't be used but I would not take it personally myself because it's a heck of alot easier than saying..this ex and that ex and her ex's ex or blah blah blah.. that gets really confusing after a while.
As for the DA I'm not sure. Sometimes in small places they get involved if there is no centralized collections for child support, I think. They don't do it here but I've heard of them getting involved in child support cases before. Do you know what the matter is regarding concerning the DA?