N.Y. CPLR 1201
Unless the court appoints a guardian ad litem, an infant shall appear by the guardian of his property or, if there is no such guardian, by a parent having legal custody, or, if there is no such parent, by another person or agency having legal custody, or, if the infant is married, by an adult spouse residing with the infant, a person judicially declared to be incompetent shall appear by the committee of his property, and a conservatee shall appear by the conservator of his property. A person shall appear by his guardian ad litem if he is an infant and has no guardian of his property, parent, or other person or agency having legal custody, or adult spouse with whom he resides, or if he is an infant, person judicially declared to be incompetent, or a conservatee as defined in section 77.01 of the mental hygiene law and the court so directs because of a conflict of interest or for other cause, or if he is an adult incapable of adequately prosecuting or defending his rights.
N.Y. CPLR 1201