How does childhood obesity occur?

This question truly haunts me, how do parents allow their child get to the point that it is unhealthy? Im asking this question because as a parent you control what your child is eating is not like they are a college student on their own. I want to know more about this topic because I feel like obesity is an obstable that could potentially be tackled much easier than a life long harmful memory or trauma.
After reading 'How Does it Happen?' The reasonings are clear. The way the parents are and their influneces on the family. The way the child eats and the amount they eat could be a problem. Some children are just naturally lazier than others and genuinely enjoy relaxing activites. These relaxing activites usually include TV. TV and gaming systems are a huge contributor to childhood obesity. The article explains the amount of time children spend infront of a TV is unhealthy. They choose to sit down rather than go outside and play. When I was little my brother and I were out until the street lights came on.
As a teacher there is not much that I can do about a childs weight because I am not there cooking for them. However as a future parent I can make sure my child is eating in proportion and physically active. I do not want my child in front of the TV all day doing nothing. I want him/her out like I was as a child, experiencing the great outdoors.

Childhood Obesity Link

Obesity Cycle Link