Wash. Rev. Code § 26.33.430
The court, in reviewing and approving an agreement under RCW 26.33.295 for the adoption of a child from foster care, shall encourage the adoptive parents, birth parents, foster parents, kinship caregivers, and the department or other supervising agency to seriously consider the long-term benefits to the child adoptee and siblings of the child adoptee of providing for and facilitating continuing postadoption contact between siblings. To the extent feasible, and when in the best interests of the child adoptee and siblings of the child adoptee, contact between the siblings should be frequent and of a similar nature as that which existed prior to the adoption. If the child adoptee or known siblings of the child adoptee are represented by an attorney or guardian ad litem in a proceeding under this chapter or in any other child custody proceeding, the court shall inquire of each attorney and guardian ad litem regarding the potential benefits of continuing contact between the siblings and the potential detriments of severing contact.
RCW 26.33.430