I have to make a life insurance decision before the end of this year and the life insurance thread made me curious how/if anybody includes social security in their plans?  
If I was in my 20s I would not plan for it, but for some people it seems short-sighted to not include it.  

Specifically for my situation: One of our kids is disabled and will never be able to live independently, he is 17 years old.  SS website says he will be eligible for some SS disability benefits once he turns 18.  
If I die next year, based on my reading of the SS website, the wife would be eligible for some of my SS benefits immediately because:
It's difficult(impossible by design?) to determine an accurate amount of what the SS benefits would add up to, but they are all individually 59-100% of my full retirement amount.  SS website says:
That's a significant amount of monthly income from SS no matter when I die.
Is it foolish for me to include SS benefits when considering how much life insurance I should get?

It's not foolish.  SS benefits may change, that would be my concern.  But, if you do count them, you might be able to purchase less insurance and invest the savings where you would get a higher rate of return.  Too many variables to predict what would be best.

Do you have a financial planning document to estimate how much money your family would need?

Plug in an estimate of social security and then you will have an idea of how much of a gap you would need for life insurance.

You can do a sensitivity analysis by varying the SS payments to see how that impacts the gap your insurance would have to cover.

Your plan should be updated periodically as life changes and maybe your house is paid off, lowering your monthly costs,

The more sophisticated tools have the ability to factor in inflation.