Last summer we went to Crystal Mountain Resort in Northern Michigan. We did not go at a peak time of the year so it was not crowded - not sure how it is when it is packed. Strangely, we were just planning on sleeping there as we planned to go to Sleeping Bear Dunes, visit lighthouses, go hiking and canoeing, etc. But once we arrived at the resort we found things to do there too. Our children were 7 and enjoyed the alpine slide, the pool (which w/b good for younger children), the art park, etc. They also enjoyed the things we did outside the resort like hiking, beach, etc. I think it would be a nice place to go with extended family. During peak season, they have more children's activites by age groups. It’s not ‘crunchy’ but you can enjoy the more outdoorsy parts of the resort and visit the small towns and state parks in the area surrounding the resort. There seemed to be something for everyone. We did not take advantage of the spa but my 77yo mom said she would love to go next time and spend her time golfing and going to the spa.
When the kids were six we rented a house in Seaside in Florida. My cousins go often with extended family and love it. We did not care for it. It was too ‘stepfordish’ for us. (Maybe it w/b better with a larger group.) But, it is near the ocean and you might like it. It seems as though they have a lot of activities for the kids to do while the parents do other things. This was something we were not interested in but my cousins really like it and since they go often, their kids are very comfortable there on their own.
We are also fans of state/Nat'l parks. If you want to canoe, hike, ride horses, swim and then just do puzzles or play games at night...many state parks have those options. In our state, the accommodations are old and the food is horrible (so we look for small local eateries) but we've had fun. Even as young as age four our children enjoyed the hiking, ranger activities, etc. We enjoyed Turkey Run State Park in Indiana http://www.turkeyrunstatepark.com/ and Mammoth Cave in Kentucky http://www.nps.gov/maca/index.htm and Mackinac Island in Michigan http://www.mackinacparks.com/mackinac-island-state-park/. (Two days is long enough for us at Mackinac Island.) We tend to visit the parks at off-peak times...we are not fans of crowds.
Several of our neighbors take extended family vacations to Disney World and love it - they go every year; sort of like a family reunion. We went with our children (not extended family) and did not care for Disney World . (I hesitate to say that since so many people love it.)