Massachusetts General Laws Part II. Real and Personal Property and Domestic Relations (Ch. 183-210) Ch. 209C, § 26

(a) In a proceeding to adjudicate competing claims of, or challenges to, parentage of a child by 2 or more persons, the court shall adjudicate parentage in the best interest of the child, based on: (i) the age of the child; (ii) the length of time during which each person assumed the role of parent of the child; (iii) the nature of the relationship between the child and each person; (iv) the harm to the child if the relationship between the child and each person is not recognized; (v) the basis for each person's claim to parentage of the child; and (vi) other equitable factors arising from the disruption of the relationship between the child and each person or the likelihood of other harm to the child.

(b) If a person challenges parentage based on the results of genetic testing, in addition to the factors listed in subsection (a), the court shall consider: (i) the facts surrounding the discovery that the person might not be a genetic parent of the child; and (ii) the length of time between the time that the person was placed on notice that the person might not be a genetic parent and the commencement of the proceeding.

(c) The court may adjudicate a child to have more than 2 parents if the court finds that it is in the best interest of the child. A finding of best interest of the child under this section does not require a finding of unfitness of any parent or person seeking an adjudication of parentage.

(d) Custody, parenting time, visitation and child support shall be determined in accordance with applicable laws, rules, regulations, orders and guidelines.