I've known two people in the medical field in this position, late stage cancer with young children at home. Both chose to fight with drug cocktails and experimental treatments (such as sipuleucel-T when it was in trials) but stopped short of life debilitating treatments like chemo, although one was lucky enough to get laser based irradiation therapy (I forgot the technical term, but it uses an accelerator to irradiate a tumor without harming surrounding tissue as much as chemo: http://www.protons.com/protons/index.page). I never asked but I'm guessing that they've seen all too often what the family goes through with a loved one dying from terminal cancer and don't think it's worth the pain or suffering, for the family or for them.
It's a hard tradeoff. Maximize the quality time you have, and prepare for your family's future -- especially before the diagnosis comes.