I think what you want to be doing, to show that these are real wages for services performed, is to pay a similar wage to what you would pay an unrelated person for similar duties, and to ensure the child is actually capable of performing these duties. For example, if your child is helping you with bookkeeping and billing and invoicing, for three hours a week, it would probably not be well reviewed by the IRS if you were paying them $1000 a month for 12 hours work.
