I don't practice in WA but in general many states have now have victim's rights laws. If they exist in WA you should be able to make a statement at your ex's sentencing. He was after all endangering the child and it wouldn't hurt to remind the judge and DA of this. Call the DA to see whether they have an office of victyim's rights or something similar. That's your best starting point.
In answer to your first question regarding the right to address the court at sentencing I would direct you to the web-link that I have provided below.
Question a): Requests to address the court by persons other than the defendant may be made through the prosecutor's office but may also be facilitated through defense counsel.
Question b): The marital status does not affect my anwser.
Most judges will allow individuals, especially parents of a minor child to address the court prior to sentencing. Make sure and let the attorney representing your child know of your wishes. I highly doubt the court would deny you the ability to address it. I don't believe the marital status woudl affect the court's decision, but you would want to be sure and not verbally disrespect the court or others while offering your thoughts. Good luck.