If the child is under the age of 13 there is no benefit for indicating they are disabled.
This is the IRS definition of permanently and totally disabled -
Permanently and totally disabled. Your child is permanently and totally disabled if both of the following apply.
• Your child 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.
