If a child is age 18 or older
Yes they are
Unfortunately, no relevant information is found.
What happens if the adult child get married/
Has  he or she receivesd benefits as an adult disabled since childhood
yes
the benefits generally end if he or she gets married
Concerning eligibility for retirement benefits .  Are there any other restrictions?
If you are also eligible for retirement benefits but have n't applied yet ,  you have an additional option .You can apply for retirement or survivors benefits now and switch to the other higher benefit at a later date
Also, what if the adult child is already receiving some SSI or disability benefits on their own record? are there more benefit options?
benefits may be payable on a parent 's earnings record . Higher benefits might be payable and entitlement to Medicare may be possible
Is there a phone number I could use to get this benefit information if I have hearing issues?