Here are some ideas you can help your kids get exercise in the warmth and safety of their own home:
Indoor climbing walls offer a chance to build muscles, increase balance, enhance flexibility and climb to new heights. For the kids, you don't have to build the side of a mountain. A simple frame with holds attached and a mat at the bottom can keep your little monkeys having a ball. Find detailed plans at www.indoorclimbing.com. If the sky's the limit money-wise, hire someone to build your wall. Check locally or go to a firm like American Rock Climbing or Rockwerx.
Compact kids' indoor gyms may be a bit more down to earth in price and skills required to make them. There are a number of companies with some sturdy, swinging options. The basics include metal and rope ladders; sport rings; trapeze bars and climbing ropes. They are relatively easy to install and are created so they don't leave marks when you take them down. For less than $200, you can find a basic model with quite a few bells and whistles at the Dream Gym store. Limikids and Home Gym for Kids also have some affordable and small-space friendly options.