Its impossible for me to overemphasize the impact the USDS can have, the question is never "will somoene let us do this" its always do we have the resources to do what needs to be done. What will crush you is the burden of service, and knowing the only thing limiting the impact you have is the amount of work you can physically put into it.
In terms of pay, I have kids and was a single income during my tour of duty. Its a better life then most Americans will live, so while your quality of life will not be as high as it may be on a private sector job, you won't be lacking anything you need.
> this comment is overemphasizing the impact a lone engineer working on a government project will have, which will just disillusion and frustrate applicants once they start the job.
Very reasonable assumption! However, that's not the USDS model. The work can certainly be frustrating but people aren't dropped in alone. We maximize the impact of our work.
The parent's concerns about quality of life with pay topping out at 160k is real and shouldn't be waved away with "it's worth it". Doubly so if you have kids. Take a look at this recent living wage page: http://livingwage.mit.edu/. Can you make it work? Sure. But going into this with eyes wide open is better than looking at this with rose-tinted glasses.