As Camp said, a permenantly disabled child still follows the "Qualifying Child" rules.  So if the 'child' lived with the father for over half of the year and did not provide over half of his own support, it seems like he DOES qualify as a dependent.

However, the Standard Deduction for dependents is different, so the dependent will have "taxable income" (after the Standard Deduction) and will need to file a tax return.

Although many people seem to improperly ignore this, it is quite possible that the 'child' had more than $1820 of gambling income.  He needs to report ALL gambling income, not just the ones that are large enough to be on a W-2G.