Just to clarify: are these social security survivors benefits the child in question is receiving? If so, then those benefits may be subject to tax depending on how much other income the child had. If the benefits, plus any other income, exceed the filing threshold, then the child will have to file a tax return. The IRS has a page on its website that discusses some of the basics on how survivor's benefits are taxed here: http://www.irs.gov/Help-&-Resources/Tools-&-FAQs/FAQs-for-Individuals/Frequently-Asked-Tax-Questions-&-Answers/Social-Security-Income/Survivors'-Benefits/Survivors'-Benefits
See if that information doesn't help to resolve your question.
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