Wash. Rev. Code § 26.26A.435
(1) A proceeding to determine whether a presumed parent is a parent of a child may be commenced:
(2) A presumption of parentage under RCW 26.26A.115 cannot be overcome after the child attains four years of age unless the court determines:
(3) Except as otherwise provided in RCW 26.26A.465, the following rules apply in a proceeding to adjudicate a presumed parent's parentage of a child if the woman who gave birth to the child is the only other individual with a claim to parentage of the child:
[ 2018 c 6 s 508.]