if married, the child (your husband) must not have filed a joint return. however, if the only reason for filing a joint return is to claim a refund for taxes withheld (see IRS PUB 501)where there is no (joint) tax liability he meets one of the tests to allow his parents to claim him.
there would likely be a tax liability (line 16) if your joint taxable income was in excess of your itemized or standard deduction. in this case, the only way the parents could claim him is if each of you filed as married separate. you and your spouse are the ones to decide
