Kids' Eating: Putting a Child on a Diet
Under 10 is too young. If your child is overweight, your family pediatrician can get involved either to help prevent more weight gain or to lose a very small amount of weight over time. But again, your kid's eating should be altered only under the advisement of your doctor.
If your child is not overweight on the physician's percentile charts, but you're concerned about his eating habits, perhaps you can talk to him about the kinds of healthy foods he would like to have in the house. This can be an opportunity to improve the health quotient of the food your child eats, even though dieting itself should be discouraged. Helping your child feel comfortable with his body is important at this age.