Generally, it is not thought that genetics alone are responsible for childhood obesity, because the rates of childhood obesity have increased significantly in the last few years without any major change in genetics. Genetics may play a role in the ability to gain weight in some children though.
Behaviors are thought to be an important part of becoming overweight or obese. Eating behaviors such as large portion size, unhealthy food types, eating meals away from home and drinking sugar-rich beverages are some of the contributors to becoming overweight. Physical activity, or lack of it, is an important factor in determining how many calories are spent or stored in the body as fat. Children are just not as active as they used to be. Video games, televisions, computers and mobile devices have replaced outdoor play and group sports. This is an important problem in childhood obesity. Social norms also contribute to this problem. If your child eats the same way as his/her friends and has a similar body type, you may not think of him/her as overweight or obese. If the society is overweight as a group, it is difficult to identify one child as being overweight. Parenting is another important contributor to childhood obesity. If a parent or both parents are overweight, the risk of a child becoming overweight or obese increases greatly. Making an effort to lose weight yourself if you are overweight, and monitoring your child's eating behavior is an important behavior change in helping your child's weight.
Children are greatly influenced by their environment and by other children. What children do at school, daycare, afterschool programs, and in the community affects what they eat and their physical activity level. Children spend long hours away from home and are learning some of their behaviors outside of the home.