Do you mark disabled for minors who are Autistic and ADHD?

It depends on the severity of the condition. 

 

The IRS defines a disabled person as one who cannot engage in any substantial gainful activity because of a physical or mental condition. 

 

This is the same definition used by the Social Security Administration. If your child gets Social Security Disability, you can rely on that as proof of disability.

 

Otherwise, the question of disability is a medical question and should be posed to your child's doctors. 

 

It's worth noting that you don't get anything extra on your tax return for a disabled dependent until they are over 17 years of age. 

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.