1. Walking has been shown to boost immunity in fact lower the number of sick days, this was reported this week by The Appalachian State university. Walking 45 minutes 5 days a week was all it took for the effect.
2. It decreases your risk of cancer, a study done in 2560 Finnish men followed for 16 years found that men who were moderately active for 30 min a day had 50% less chance of developing cancer.
3. It helps you get a better nights sleep and evidence shows that good sleep is vital for maintaining a healthy weight.
4. It helps keep blood sugars in check, in fact if you have type 2 diabetes exercise is a wonderful tool to keep your blood sugars under control.
5. Its fun and can be a great family activity, playing tennis together, going to the pool, skiiing, dancing around the house!

References:

1. http://www.chowandchatter.com/2009/07/your-daily-workout-can-decrease-your.html
2. http://edition.cnn.com/2006/HEALTH/diet.fitness/06/20/hb.exercise.benefits/index.html
3. http://online.wsj.com/article/SB10001424052748704350304574638331243027174.html?mod=WSJ_hpp_MIDDLENexttoWhatsNewsThird