Family Law Questions? Ask a Family Lawyer Online.
You will want to petition the courts for custody based on the best interest of the child. I would advise you to hire a lawyer as they can get a emergency hearing in quickly and see if the judge will grant you custody based on the living arrangements of the child.
If this is not a possibility to hire a lawyer you will need to fill out the forms at the following link: Washington Courts Fill them out completely and submit them to your local clerk of courts office with the filing fee's. The clerk will help you get the paperwork needed to serve the father and will set up a hearing for a temporary custody order to address who should have custody and the right to file.
I wish you the best,