Non-parental custody (once upon a time known as third-party custody) is where you seek to become custodian of children who are not your own. The law governing these cases is RCW 26.10. The controlling idea is the best interests of the children. Specifically, the person bringing this type of case is seeking to prove that the biological parents are unfit, or even if fit, it would be an actual detriment to the children to live with these parents. There is nothing that defines what is an "unfit" parent. One useful way to present the case to the court is show how the parents are unwilling or unable to perform parenting functions, using the statutory definition of parenting functions (see link below). A court is not required to adopt this approach, but it is very tempting for the court because it is a clear list and relates to the statute.
All of the necessary forms are on the Washington State Courts website. It is better to have a lawyer, but if you have to do it yourself you can use the courthouse facilitator to make sure you've gotten everything filled out correctly. It is better to give the court too much information rather than too little. But instead of telling a long drawn-out story highlight what your concerns are (i.e., drugs, DV, etc). Also, if there are children who all have the same mom and dad, file just one petition covering them all. If there's more than one mom and dad, file a separate case for the children according to who they belong to. For example, dad has two kids by two different women (kids were living with dad and the mom of one kid) so you would file two separate cases (child 1, you vs. dad and that mom AND child 2, you vs dad and the second mom) because each child's case may have a different outcome (one child stays with you, other child is sent to live with second mom, dad gets no kids).
In non-parental custody cases, petitioners (and everyone in their home over the age of 16) are required to have a Washington State Patrol background check done. It's quicker and cheaper to get it done online. You (and everyone over 16 living in your home) also have to have a DSHS background check too. There's an order the court has to sign (you want to get it signed when you first file your case) to order DSHS to release any records they have. Get these requests underway quickly. It's unlikely that you'll have all the results by the time of the first court hearings. That's okay. Note that every time you have a court hearing, the court will run a JIS (Judicial Information System) background check on every adult in your home. Make sure you have the full legal name and date of birth of every adult in your home handy each and every time you go to court. JIS shows everything in WA, criminal and civil. This includes traffic stuff. Yes, the other parties have have a JIS too.
Ex Parte Restraining Order
Usually, these cases start with an ex parte restraining order because as soon as the parents are served, they'll want to come scoop up the kids. This is where having a lawyer really really helps. The court will read through your papers, run the JIS and likely sign an order keeping the kids with you until the initial hearing. Make sure you have someone to serve the parents promptly with the ex parte restraining order. Make sure that the childrens' school, daycare have a copy of it as well as make sure neighbors are aware of what's going on.
This is the initial hearing with everyone present. The court usually will be addressing the restraining order as well as whether there's adequate cause to proceed with non-parental custody. The court may appoint a Guardian ad Litem, order substance abuse testing/assessments, and visitation. The ruling by the court about visits, etc, will likely remain in effect until the Guardian ad Litem's report is filed. So, if there's any potential problems with the court's ruling, address it openly to the court right then. Problems that arise will often have to wait for the GAL report. One thing to keep in mind throughout this process is that non-parental custody is NOT about who can provide the better home. Being poor is not the same as being a poor parent. The focus is always on the ability of the biological parents to provide a safe, stable and appropriate home. Don't let the case become about poverty, its a powerful weapon for biological parents.