(1) In a proceeding under this chapter, a petitioner seeking to establish a support order, to determine parentage of a child, or to register and modify a support order of a tribunal of another state or a foreign country must file a petition. Unless otherwise ordered under RCW
26.21A.255, the petition or accompanying documents must provide, so far as known, the name, residential address, and social security numbers of the obligor and the obligee or the parent and alleged parent, and the name, sex, residential address, social security number, and date of birth of each child for whose benefit support is sought or whose parentage is to be determined. Unless filed at the time of registration, the petition must be accompanied by a copy of any support order known to have been issued by another tribunal. The petition may include any other information that may assist in locating or identifying the respondent.
(2) The petition must specify the relief sought. The petition and accompanying documents must conform substantially with the requirements imposed by the forms mandated by federal law for use in cases filed by a support enforcement agency.