The current order of child support remains in place until it is changed. If the mother wants to claim child support, she needs to file an action with the court to get child support changed. If she just lost a petition to modify the parenting plan and your 18-year-old is moving back in with you, then she would have no basis to modify child support for future months.
If the 18-year-old is still living with his mother, then she would need to file a petition to modify child support to begin collecting child support payments.
Nicole M. Bolan, Attorney at Law
Blado Kiger Bolan, Tacoma, Wash.