If my son collected SSI as a child and now is waiting for his adult disability decision do I list him as disabled or not?

Disabled for tax purposes must follow the IRS rules for determining being permanently and totally disabled -

Permanently and totally disabled. Your child is permanently and totally disabled if both of the following apply.
• He or she can't engage in any substantial gainful activity because of a physical or mental condition.
• A doctor determines the condition has lasted or can be expected to last continuously for at least a year or can lead to death.