There are some kids out there who don't like keeping fit regularly, which I find quite odd seeing as kids normally love to go outside and run around and play. So, here's a well prepared guide on how to encourage your children (if they are lazy) to exercise.
Don't set a specific time - setting a specific time for the kids to exercise will only make them despise it more. Instead, do it at random times of the day, or on the weekends.
Buy a whole bunch of new stuff to exercise with - when I say "exercise" for children, I don't mean stationary bikes and cross trainers. So buy new soccer/footballs, netting, tennis raquets, frisbee's, hula hoops and skipping ropes so they have a lot of choice.
Laziness is a habit - kids become lazy due to it becoming a habit. Your child comes home from school, gets on the xbox, then watches a movie and then sits in bed and plays DS until its time for dinner. Snap them out of these habits and take away consoles if necessary.
Clubs & Activities - Older kids and even the younger ones can benefit from joining a sporting group. Groups such as Aus-kick, tennis lessons, local soccer clubs, gymnastics and dancing all make a positive impact on your child's life. They may take a while to find what activity is best for them.
Active kids are happier kids, children who do not exercise will more likely be grumpy, irritable and lazy. Getting physical activity with the kids also motivates them a lot.