In any civil proceeding had pursuant to NRS 432B.410 to 432B.590, inclusive, if there is expert testimony that a physical or mental injury of a child would ordinarily not be sustained or a condition not exist without either negligence or a deliberate but unreasonable act or failure to act by the person responsible for the welfare of the child, the court shall find that the child is in need of protection unless that testimony is rebutted.
NRS 432B.450