If you already have a parenting plan, then she has to comply with it or you can file a motion for contempt. If you do not have a parenting plan, then you need to file a petition for a residential schedule. It's not up to the ex if you get to see your child. Also, the fact that you are paying child support does not mean that you get visitation. The obligation to pay support is not connected to visitation. If you weren't paying she would still be obligated to follow a parenting plan.
Don't make child support payments directly to the other parent unless that's what your order says, and even then make sure you get receipts. Anytime you buy stuff for the child, unless you get a receipt identifying the stuff you bought as a contribution to child support it's nothing more than a gift.
If you are paying $25 per month, that's the most minimal amount under Washington law. DSHS is not going to buy off on you being a stay at home dad. Basically it's you saying the child I have now is more important to me than the one I chose to make 5 years ago. In this economy, staying at home with a child is a luxury most people cannot afford.
I sympathize with you ex about the money, but I sympathize with you about getting to see your child.
1. Child support is totally unrelated to your question about contact with your child, so I won't address the support issue.
2. The best route to renewing contact between you and your child depends on the history of contact. If you haven't had contact in a long time, I would expect a court to want to phase in increasing levels of contact over a period of time so your child will be comfortable with your relationship.
3. I'm not sure what procedure caused an end to your contact with the child. Was it a protection order, restraining order, no contact order, or modification of a parenting plan? Was it ex parte? Did you have notice? Did you appear and present testimony? Did you file a declaration? Were you married to the mother and now divorced? If not, was there a paternity action? Are you on the birth certificate? Did you sign an affidavit of paternity? Is there anything pending? No one can advise you without knowing.
4. If the mother alleged that you might physically harm the child, it is not a surprise that the court would be cautious. There's no way to know why the commissioner didn't believed you, but it sounds like the commissioner found her claims believable. If she made a credible claim that you were using drugs and a test confirmed THC (marijuana use), a commissioner is likely to require a chemical dependency evaluation and proof of compliance with all recommendations. Marijuana use is not viewed favorably by the family law commissioners. Until that time, expect supervised visitation (at best).
5. I know you don't want to hear anything negative, but some of this is hard to deal with and you need to know that. Your best bet is probably to obtain an evaluation showing you don't have any problem with drugs. I would also consider filing a petition to modify the parenting plan. If you don't have a parenting plan, you can petition to establish a parenting plan.
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