I would presume that if the support owed is greater than the $1,200 that the payment would be garnished, but if less than that amount is owed that the non - custodial parent would get a stimulus for the remaining balance. According to an article on USA Today that I'd found through Google Search the headline had said " Behind on Child Support? You won't get a stimulus check". It looks like if there is a remaining balance a check would be issued for that to the non - custodial parent. The CARES act doesn't suspend child support arrears. Hope that helps.
