Do I get a credit or deduction if my child is disabled?
If your child is older than 12 and you need to pay someone to take care of him while you work, you can say he is disabled and you can still get the childcare credit on your federal return. Or if he is 19 or older you may still be able to claim him as a qualifying child dependent on your federal return.
Aside from those things, there is no federal tax advantage to saying that your child is disabled. Your state tax laws might be different.
For disabled adults:
There is an extra amount added to your standard deduction if you are legally blind. Your federal return does not provide any other credits or deductions for saying you are disabled, with one possible exception.
There is a credit for the Elderly and Disabled which is so small that very few people benefit from it—-it has not been updated/increased by Congress for decades.
ELDERLY OR DISABLED CREDIT https://www.irs.gov/help/ita/do-i-qualify-for-the-credit-for-the-elderly-or-disabled
There are some states that provide various credits to elderly/disabled folks, so watch for that when you prepare your state return. The states that I know of that have anything for elderly/disabled are AZ, CT, DE, IA, MO, ND, NJ, NY, VE. There may be others.