The Yurts at Maine Forest Yurts are open year-round, but this trip is especially good in the winter. The wonderful people at Maine Forest Yurts in Durham will take most of your stuff into the yurt by snowmobile, so you can just focus on moving your crew along the 1 mile path on foot/snowshoe/ski. The inside is perfectly comfortable for the six of us +2 dogs, with a warm wood stove and clean (but very cold) outhouse just outside the door of the yurt.
The first time we went, none of our kids had skied before, so we snowshoed in with the youngest in a backpack. We brought along skis and were amazed at how much everyone enjoyed learning to ski right there beside the yurt. The whole property is a long sloping wooded hill with lots of trails (ungroomed), so it's great for beginners.
Now that the kids are older we can ski further, so we'll ski down the long hill out onto Runaround Pond. You can make a nice loop down one of the Maine Forest Yurts trails, along the pond, and back up another trail. Just confirm with the staff that the pond ice is safe when you visit.
Book early because the yurts fill up fast. We first did it with kids ages 3 to 11 and have gone back several times since.
Side note: My best advice is, don't get the stomach flu while staying in a yurt. I can promise you it's one of the most miserable evenings you'll ever have.