If your husband’s child support is in arrears, then your joint-return tax refund and most likely the stimulus payment will be applied to the amount owed.
However, you might consider filing what's known as an Injured Spouse Allocation, as you suggest. You can file this form even after you've filed your return, and it can result in recouping the "Injured Spouse's" portion of the refund.
For more information, please see the TurboTax article "What is IRS Form 8379: Injured Spouse Allocation".
Then, see What if I've already filed my tax return? in the TurboTax Help article “How do I file Form 8379, Injured Spouse Allocation?” for guidance.
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