According the Supplemental Security Income website (http://www.ssa.gov/ssi/text-eligibility-ussi.htm#disabled-ch...):
An individual under age 18 is "disabled" if he or she has a medically determinable physical or mental impairment, which:
-results in marked and severe functional limitations; and
-can be expected to result in death; or
-has lasted or can be expected to last for a continuous period of not less than 12 months.
It seems pretty vague to me. I have to imagine that the pharmaceutical industry not only supports this type of subsidization, but that fraud is probably a real issue.
I am certain that I could have been medicated as a teenager, and I am very glad today that I wasn't.