There are many things that a parent can do to keep their child from
becoming obese, including:

Respect your child's appetite; children do not have to finish
everything on their plate, or finish the entire bottle.
Avoid pre-prepared and foods with extra sugar.
Provide your child with a healthy diet, 30% or fewer calories from
fat.

Provide enough fiber.

Limit the amount of high-calorie food kept in the home.

Enjoy physical activities as a family (walking, playing outdoor
games, etc.)

Limit TV viewing.

Do not reward completion of meals with sweet desserts.

Replace whole milk with skim milk at about 2 years of age.
 
Encourage your child to participate in active play.