A common law marriage may not be formed by persons living within WA. If a common law marriage is validly formed under the laws of some other state, WA would recognize the validity of the marriage.
While there may not be a marriage, persons who meet the requirements may form what is formerly called a meretricious relationship in WA. WA courts currently call the relationship a "committed intimate relationship". However, case law likely is still indexed under the old name. Persons living together like a husband and wife may have property rights in properties that would have been community properties had they been married with each other. The genders of the persons involved are not relevant. Whether there is a meretricious relationship depends on the couple's specific facts.
With dependent children, there may be issues of child support and child custody (called a parenting plan in WA).
The quickest way to find legal information likely is to review your specific facts with your attorney. If you cannot get an attorney or do not want an attorney, you can do research at the county's law library at the county's superior courthouse.