S.G.
We like to head up to Oklahoma. Only 2 to 3 hours depending where you go in Oklahoma. We usually go to Arbuckle Wilderness, Route 66 for Kids, Tiger Safari, Frontier City Theme Park, Beavers Bend State Park (train rides, hay rides) and sometimes we rent a cabin with Broken Bow Luxury Cabin Rentals depending on how many rooms you want, internet access or hot tub for your family can range from $105 a night to $235 a night. http://www.brokenbowluxurycabinrentals.com/index.html
Here is the link to find some additional family activities in Oklahoma.
http://www.travelok.com/family_activities
There is so much to do in Oklahoma and its a quick drive unlike driving to Austin or San Antonio that is 6 hours for us to drive (we love these places too) as well as driving to padre island but our toddler gets squirmish which causes us to do many stops to stretch legs; our teenager on the other hand doesn't care where we go as long as we have fun and she has her ipod.
I hope your find some place that your entire family will enjoy.