Go with the hotel with pool idea; hey Mario, she lives in Michigan and the kids and she have probably had enough outdoors already this winter! You didn't say how old the kids are, but if there is a city near you that has a Children's Museum (if your kids a real young) and/or a Science Museum, you've got it made! We did the winter getaway to a hotel with pool when our kids were younger and the winters caused cabin fever; but we also live in the Twin Cities where we had membership to the Science Museum and would also go to the Children's museum (when the kids were young); either of which were great for keeping the kids busy all day long. And ordering in Pizza Hut or Domino's for supper by the pool is a lot cheaper and more relaxing than eating out with kids, too. If you decide to eat out, it's cheaper to eat out with kids for lunch than supper!
(and the kids are usually better behaved at lunch than supper,too). We took our kids to eat in the Space Needle restaurant for lunch once when we took a train trip to Seattle and it was fairly reasonable, and worth it for the memories.
PS Mario, it IS fun to winter camp; but by March, everyone is fairly SICK of winter when you live in the more Northern climes! Your idea would be great in November or December, though.