You don't say where your family is now, so the question arises:
Do you like hot weather? I mean HOT where you can fry an egg on the hood of your car in the summer? Yes, winters are great, but there's the summer...and the cost of running and repairing the A/C and driving, driving, driving, freagin everywhere...If not, choose DC.
Do you HATE the winter? DC's is not that bad, but Dallas's is better!
Do you have a strong political affiliation? If you are on the liberal end, you might get aggravated a lot and not enjoy your neighbors much in Texas. If you are on the conservative end, the opposite. We like to think it won't matter, but it is a factor in our happiness, especially if it is a strong affiliation. I received a great job offer in the deep south and just couldn't do it...
Is one of your family goals to become financially independent ASAP? If so, with higher salaries, it can usually be achieved more quickly (percentage of income of, say $90k versus $50K..."everything else being equal") in a high income state.
If square footage is the priority, then it's an easy choice (Dallas)!