The question does not affect your return if the child is not of employment age. You can answer "no" since it does not really apply. The definition by the IRS is: You have a permanent and total disability if you cannot engage in any
substantial gainful activity because of your physical or mental
condition. A 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.