Yes, disability benefits can be taken for child support.

But this only applies to Social Security disability benefits. SSI recipients will not have their monthly disability benefits and past due benefits (backpay) seized.

The reasoning applied by the federal government is this: since SSI is essentially a public welfare benefit and does not derive not from a claimant's earnings record, SSI benefits cannot be taken for other purposes, just as food stamps and AFDC funds, likewise, cannot be seized.

taken from http://www.disabilitysecrets.com/can-disability-benefits-be-taken-for-child-support.html 

As to your pension from the military you should know that up to 65% of a retired military member’s retired pay can be garnished for spousal and child support.  FOr more information please review the USFSPA

I hope this help you