257.02 SURRENDER OF PARENTAL RIGHTS.
No person other than the parents or relatives may assume the permanent care and custody of a child under 14 years of age unless authorized so to do by an order or decree of court. However, if a parent of a child who is being cared for by a relative dies, or if the parent is not or cannot fulfill parental duties with respect to the child, the relative may bring a petition under section 260C.141. Except in proceedings for adoption or by a consent decree entered under section 257C.07, no parent may assign or otherwise transfer to another parental rights or duties with respect to the permanent care and custody of a child under 14 years of age. Any such transfer shall be void.
257.025 CUSTODY DISPUTES.
(a) In any custody or parenting time proceeding involving unmarried parents, the court shall consider and evaluate all relevant factors in section 518.17, subdivision 1, to determine the best interests of the child.
(b)
The fact that the parents of the child are not or were never married to each other shall not be determinative of the custody of the child.
(c) A person may seek custody of a child by filing a petition or motion pursuant to section 518.156.
Here is some other really good info on establishing who the legal parent is/isn't:
https://mn.gov/dhs/people-we-serve/c...-parentage.jsp