@ElizaBennett - I certainly see your point, although some kids are serious enough athletes that they may be self-motivated to exercise on a treadmill in bad weather.
I have a friend who has a Tony Little Gazelle in her living room and not quite enough places for everyone in her family of five to sit comfortably. One of her school-age children usually ends up sitting on the carpet or on the step up (it's one of those slightly sunken living rooms) but often one of them will hop on the Little Gazelle and fool around for a few minutes.
She got it or herself, but it gets her kids a little extra exercise, too. It is small enough for them to use safely while being big enough for adults, and they seem to find the swinging motion to be a novelty. But they tend to hop on and off in five minute bursts!