We have several sizes of tarps (giant for longer stays down to medium for touring) that we set up over the camper extending out the back and over the kitchen which gives us a good sized dry area for table and chairs etc...
It's quicker and easier to put up than the whole annexe, but then again our annexe is ginormous and quite heavy (from back in the day of 15ounce canvas, when heavier was better).
The tarp in the picture isn't our biggest, so if you go huge, the kids will have loads of room. Maybe gazebos come in huge as well?
Anyway, I thought the first few years of camping always had to be spent in the rain so that Mother Nature weeds out those not suited to the camping lifestyle, leaving more campsites for those of us who passed the test
Good luck and happy camping