One of the challenges of living in The Great White North is keeping kids active during the winter. They each have a 30 minute dance class during the week, and they are always trying to get me to take them swimming, but I have had trouble getting them to be active on a daily basis. When it's not too cold, they both enjoy playing out in the snow. Unfortunately, we have far too many days when even the high temps are far too cold for outdoor playtime.
I think I have come up with a solution. First of all, I put physical activity on their daily school list. It has to be done before they can watch TV or play Nintendo. Here's the great part for winter: they can walk on our treadmill. Both kids are now old enough to walk on the treadmill without constant supervision. The incentive for them is that they can watch up to 45 minutes of a DVD as long as they are walking on the treadmill. They are happy because they get DVD time; I'm happy because they are up and moving.