My husband has two children and the oldest child recently moved with us. Does he have to pay full child support to the mom?

The parents will need to comply with the current court orders until the court changes the orders.

That one of the children has changed residence likely is a basis to file a motion with the court to ask the court to review the orders.

The mandatory pattern forms for most WA family law proceedings are free at http://www.courts.wa.gov/forms/ . There are links to instructions and self-help guides from that site.

The free online child support calculator for WA is at http://www.courts.wa.gov/ssgen/ .

Your husband should review his specific facts with his attorney if he is unsure of his legal options.

you need to comply with the existing court order until it is changed.

to change the existing order, you need to file a petition to modify the order of child support