Kidnapped child. If your child is presumed by law enforcement authorities to have been kidnapped by someone who is not a family, you may be able to take the child into account in determining your eligibility for head of household or qualifying widow(er) filing status, the deduction for dependents, child tax credit, and the earned income credit (EIC). For details, see Pub. 501 (Pub. 596 for the EIC).One imagines master liar George Costanza, scheming somehow to ameliorate a hideous tax burden, stumbling across this paragraph, then crafting a plan so untouchable by anyone with an even partially functioning morality gland that even Newman is horrified (though tempted to resort to blackmail).
Whether this would require one of the previously seen children on the show — from the morbidly ugly baby that nauseates Jerry out in the Hamptons, to the hyperactive kid Elaine found herself roped into sitting, or even Mickey the Midget reprising his role as a stand-in — would be a matter for the writers to craft into some sort of tidy, self-referential knot.