Your understanding is correct, a disabled adult child does qualify you for the EITC. It sounds like you may have answered the residence question wrong. The child must have lived with you more than half the year.
You should be getting the "did the child provide more than half his own support" question, not the "did you provide more than half his support" question.
The "did the child provide more than half his own support" question is for a Qualifying Child dependent. The "did you provide more than half his support" is for a Qualifying Relative" dependent (does not get you EITC).
There are two types of dependents, "Qualifying Children"(QC) and Other ("Qualifying Relative" in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit, student status, a relationship test and residence test. Only a QC qualifies a taxpayer for the Earned Income Credit and the Child Tax Credit (if under 17). They are interrelated but the rules are different for each.
The support test is different for each type. The support test, for a QC, is only that the child didn't provide more than half his own support. The support test for a Qualifying Relative is that the taxpayer provided more than half the relative's support.
A child of a taxpayer can still be a “Qualifying Child” (QC) dependent, regardless of his/her income, if:
- He is under age 19, or under 24 if a full time student for at least 5 months of the year, or is totally & permanently disabled
- He did not provide more than 1/2 his own support.
- He lived with the parent (including temporary absences such as away at school) for more than half the year
