(1) Except as otherwise provided in RCW 26.26A.465, in a proceeding to adjudicate competing claims of, or challenges under RCW 26.26A.435(3), 26.26A.445, or 26.26A.450 to, parentage of a child by two or more individuals, the court shall adjudicate parentage in the best interest of the child, based on:

(a) The age of the child;

(b) The length of time during which each individual assumed the role of parent of the child;

(c) The nature of the relationship between the child and each individual;

(d) The harm to the child if the relationship between the child and each individual is not recognized;

(e) The basis for each individual's claim to parentage of the child; and

(f) Other equitable factors arising from the disruption of the relationship between the child and each individual or the likelihood of other harm to the child.

(2) If an individual challenges parentage based on the results of genetic testing, in addition to the factors listed in subsection (1) of this section, the court shall consider:

(a) The facts surrounding the discovery the individual might not be a genetic parent of the child; and

(b) The length of time between the time that the individual was placed on notice that the individual might not be a genetic parent and the commencement of the proceeding.

(3) The court may adjudicate a child to have more than two parents under this chapter if the court finds that failure to recognize more than two parents would be detrimental to the child. A finding of detriment to the child does not require a finding of unfitness of any parent or individual seeking an adjudication of parentage. In determining detriment to the child, the court shall consider all relevant factors, including the harm if the child is removed from a stable placement with an individual who has fulfilled the child's physical needs and psychological needs for care and affection and has assumed the role for a substantial period.