N.J. Stat. Ann. § 9:2-16

An approved agency may take a voluntary surrender of custody of a child from the parent of such child, or from such other person or persons who, by order of a court of competent jurisdiction, have been substituted for the parent as to custody of such child. Each such surrender, when properly acknowledged in the manner and form provided by sections 46:14-6 and 46:14-7 of the Revised Statutes, shall be valid whether or not the person giving the same is a minor, and shall be irrevocable except at the discretion of the approved agency taking such surrender or upon order or judgment of a court of competent jurisdiction, setting aside such surrender upon proof of fraud, duress or misrepresentation.