If qualifed, you may claim your child as dependent, Under your child's information, there is a question in Turbo Tax, "Did any of these apply to the child"?, choose the bullet "was disabled".
In order to claim a disabled child, although age is not a requirement, a child must be permanently and totally disabled based on doctor's certification. If qualified, you may receive child tax credit and earned income tax credit on your income tax return.
[edited 3/2/2021 @ 2;47PM]
