Good info:
Topic 357 - Tax Information for Parents of Kidnapped Children
You may claim a kidnapped child as your dependent if the following requirements are met:
1. The child must be presumed by law enforcement to have been kidnapped by someone who is not a member of your family or a member of the child's family, and
2. The child had, for the taxable year in which the kidnapping occurred, the same principal place of abode as the taxpayer for more than one-half of the portion of such year before the date of kidnapping.
If both of these requirements are met, the child may meet the requirements for purposes of determining:
* The dependency exemption
* The child tax credit, and
* Head of household or qualifying widow(er) with dependent child filing status.
This tax treatment will cease to apply as of your first tax year beginning after the calendar year in which either there is a determination that the child is dead or the child would have reached age 18, whichever occurs first.
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Tax Topics - Topic 357 Tax Information for Parents of Kidnapped Children