One of my biggest woories as a parent is childhood obestiy. I see so many young children struggling with their weight and honestly society today encourages "model thin" or "electronic childen" (too much TV, video games and not enought exercise!)
Here is a great guset post:
Television and video games are another common problem with children. Left on their own children will not receive enough proper exercise to burn off excess calories. Limiting kids to one hour of television or video games a day will help guide them to more active activities. Also, try to get the child involved in sports. Many kids may be unwilling to take up sports in the beginning; however, once most children are involved they grow to love it. This can lead to further involvement in other sports and a much healthier lifestyle.
Changing the habits of a child is not an easy task. It will need a big effort and there will be relapses; however, remember it is for the good of the child. Laying a good foundation for a healthy future is one of the best things a parent can do for a child.