I never received my stimulus payments. I owe back child support, but I was never notified of that they withheld it for that reason. Should I put yes/no on recovry rebate?

Did you ever receive a letter letting you know what your stimulus payments were?  

If not, you can use the link to determine what amounts were issued to you.

View your account information with the IRS

If the IRS website indicates you received both payments, you will answer the question accordingly in TurboTax to reflect that you did receive either one or both payments, as well as the amounts, based upon your account information above.

The Recovery Rebate would only apply if you were entitled to receive the stimulus payments but never did.  If any payments were used to pay back child support, you are considered to have received the payment.

Recovery Rebate Credit eligibility