I'm on the fence about this one. While living a fit lifestyle is important, I think that fitness at an early age should consist of playing in the park or taking up a sport. I know, somewhat from experience, that if you try too hard to encourage children to become fit, they may rebel at a later point. If a child wants to exercise seriously when they become older, or if you really just want them to try, then by all means do so. My mother took me to a sample gym session, but said she would never bring fitness up to me again if I didn't like the experience. In the end I made myself exercise, not because I liked it, but because I knew it was good for me. My appreciation of fitness videos didn't come until I had been exercising for six months, when I took the initiative to try my mother's videos, without her coaxing. So introduce fitness, but don't be pushy.