In the state of Nevada, for a custody case, can we record a conversation with the children and use it in court? If we can, must we inform the children

Like much in law, two responses.  First, "it depends."  Second, you should not necessarily actually do everything you are lawfully entitled to do. If you mean live, then the answer is yes.  If you mean over the phone, then the answer is no (Nevada is a "two party consent" state not allowing one party to a phone conversation to record it without the explicit, or at least implicit, consent of the other party -- that is why so much tech support starts out with the recording "this call may be recorded for quality assurance" etc.) Assuming you are talking about a live conversation, or otherwise get clearance to make such a recording, do give some thought as to how that fact, if and when made known to the children or others being recorded, will play in their future dealings with you.  It might be wiser to use other means -- like child interviews at FMC, or even an evidentiary hearing -- to get to the truth of the matter.  Think carefully before acting.