No specific medical diagnosis constitutes disabled to tax purposes.
A child's disability doesn't affect tax filing until he turns 19 (24 if a full time student). Then his disability allows him to continue to be considered a "Qualifying Child" for tax purposes regardless of age. There are no credits or deductions, other than that some items, e.g. special schooling, can be considered medical expenses.
“The term ‘disability’ means, with respect to an individual –
(a) a physical or mental impairment that substantially limits one or more of the major life activities of such individual;
(b) a record of such impairment; or
(c) being regarded as having such an impairment.”
For the IRS, disabled means -
"an individual shall be considered to be disabled if he is unable to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment which can be expected to result in death or to be of long-continued and indefinite duration. An individual shall not be considered to be disabled unless he furnishes proof of the existence thereof in such form and manner as the Secretary may require. "
I believe the substance of that paragraph is that it is your Doctor's decision
- He or she cannot engage in any substantial gainful activity because of a physical or mental condition and
- A doctor determines the condition has lasted or can be expected to last continuously for at least a year or can lead to death.
However, the IRS defines Substantial gainful activity this way so if they have part time jobs then they are engaging in any substantial gainful activity so it would not meet the requirements.
"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. "
