There are many reasons why a parent would wish to nip an incipient obesity problem in the bud. It is as important for a child's emotional health as it is for physical health. Being overweight is one of the things other children will pick on.
Limit Screen Time : All the cuts in physical education and the increase of computer use in schools make it imperative that parents control screen time at home. This includes television and video games. Not only does it prevent the child less active it can lead to permanent vision problems.
After School Activities : Schools and other organizations can offer children organized sports to participate in. If your school district is limiting that due to budget problems check with the local parks and recreation district. They often offer classes that can help a child get plenty of exercise.
Menus : A child can't eat junk food if there isn't any in the house. Sit down with your family and write out a menu that suits everyone. Include after school snacks in this list. The child might not like fruit but enjoy hummus. I know this from experience as our granddaughter is that way.
Educate : There are two reasons to educate your child about eating and exercise. The first is that one day he's going to have to do this on his own. The second is that children want to know why they have to do or eat certain things and not do or eat others. Making a drastic change in diet is not going to be easy if the child doesn't understand why.
Make the Change with the Child : While you will have to do this at home in order to keep everyone on the diet you should extend that to outside the home. If your child knows you're skipping french fries and soda pop for a healthier meal it will make it easier for the child. It also helps your own waist line.