Hi Jane:
With three days, I would suggest visiting Magic Kingdom and Epcot for certain as, in my opinion, those Parks tend to provide the most variety of entertainment options for the whole family. There's so much to do at those Parks, especially the Magic Kingdom, that you may want to make your third day a repeat of Magic Kingdom. If you want to visit a third Park, I would likely pick Hollywood Studios over Animal Kingdom. Between the updated
Star Tours and
Toy Story Mania, Hollywood Studios is a hot Park right now. However, if your family is full of animal lovers, then Animal Kingdom may be a better option for you.
My best guess is that Park Hoppers won't be the best option for your family if you are looking to save money and reduce stress. While Park Hoppers can give your family more options, with such a large party, it may get stressful to round up the whole family to move Parks in the middle of the day.
Enjoy your vacation.