Do you have to seek child support if you separate without a formal custody agreement?

If the two parents agree to work together, in WA, there is not any law that requires the parents to take each other to court.

If the parent with the children gets any public assistance for the children, the parent likely will be required to cooperate with that office's filing of an administrative or court child support action.

Without court orders, the parents may start having arguments with each other about how much to pay and when to see the children. (Even with court orders, the parents may argue; however, the court orders may be clearer as to the rights and obligations of each parent.)

Without proper documentation, in WA, the father not married to the mother may be ordered to pay back child support up to 5 years before the date of filing a petition.

You should review your specific facts with your attorney to find your legal options.