If your child support debt is in collection status - yes - any tax refund you might expect will likely be garnished. That include regular tax refund and stimulus rebate check. You will receive a notice that states the original refund amount, your offset amount, the agency receiving the payment, and the address and telephone number of the agency.
That is according to the Treasury Offset Program authorized by Congress. Please see some details here - http://www.irs.gov/taxtopics/tc203.html