From a recent report by Social Security's Office of Inspector General:
... An SSI recipient may be eligible for CDB [Child Disability Benefits -- Disabled Adult Child Benfits or DAC is what they're usually called] as a disabled child on a wage earner’s record [the father or mother] under the OASDI [Old Age, Survivors and Disability Insurance] program when the recipient meets the criteria for benefits. To conduct our review, we identified 1,017 SSI recipients who were potentially eligible for CDB from 1 of 20 segments in SSA’s system. From this population, we selected a random sample of 50 recipients for review.
... [W]e identified SSI recipients who were eligible for CDB. Our analysis of 50 SSI recipients identified 22 who were potentially eligible for, and 15 potentially technically entitled to, CDB. This occurred because SSA did not always (1) develop and dispose of leads related to CDB and/or (2) identify SSI recipients eligible for CDB during reviews of their non-medical eligibility factors and SSI payment amounts. Separate from our review, SSA has conducted projects, which identify SSI recipients who were potentially eligible for CDB. Based on the results of our review, we estimate 8,140 SSI recipients were potentially eligible for CDB and may be due underpayments totaling approximately $18.5 million. If SSA does not take action, we estimate the 8,140 SSI recipients may lose an additional $3.6 million over a 12-month period. ...
In my experience there are two types of benefits that are very frequently missed: Disabled Adult Child and Widowers benefits. Parents benefits are usually missed but there are very, very few entitled to Parents benefits. I always discuss the possibility of DAC benefits with young disability claimants. Even if they're not eligible now because neither of their parents is on Social Security benefits or retired, they'll need the information for later. I also make a point of asking both older male and older female clients about their marital status so I don't miss Widows and Widowers claims.