Indicating a disability for a child under the age of 19 has no tax benefit. The IRS defines permanently and totally disabled as -
Permanent and total disability. You have a permanent and total disability if you can't engage in any substantial gainful activity because of your physical or mental condition. A qualified physician must certify that the condition has lasted or can be expected to last continuously for 12 months or more, or that the condition can be expected to result in death.
Substantial gainful activity. Substantial gainful activity is the performance of significant duties over a reasonable period of time while working for pay or profit, or in work generally done for pay or profit. Full-time work (or part-time work done at your employer's convenience) in a competitive work situation for at least the minimum wage conclusively shows that you are able to engage in substantial gainful activity.
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