If you’re a parent, teaching your kids about healthy eating is just one of a long list of things to check off before they leave the nest.

The good news, according to a new study, is that parents may have more influence over the amount their children eat than they think they do. And it all comes down to how much food parents serve.

Researchers from the University of Colorado School of Medicine found that parents gave their children servings of food similar in size to what they gave themselves, and the more the children were given, the more they ate. On the other hand, parents who served themselves smaller portions also gave their children smaller portions.

Better that children ask for more rather than being encouraged or forced to eat more.

“The good news,” said Susan Johnson, professor of pediatrics at the CU School of Medicine and the study's lead investigator, “is that parents influence their children much more than they may feel they do. The challenge remains as to how to encourage children to consume a healthy diet and to eat amounts that help them grow appropriately. Clearly, family habits and behaviors are both incredibly important in this regard.”

On three occasions, observers went into the homes of families recruited into the study from Head Start programs in Houston, Texas at dinnertime and took photos of the servings children and adults received. The families were asked to cook their meals as they normally would and serve it using standardized utensils.

From the photos, trained dietitians estimated serving sizes and food intake.

Some children in the study were served, and ate, adult-size portions, leading them to eat more in general, and contributing to overweight. When parents served more to themselves, they also served more to their children.

For example, a two-year-old should be served two tablespoons of chopped chicken, two tablespoons of green beans, and two tablespoons of applesauce. If they eat that and want more, that’s okay.

The study sheds light on an important concept in child nutrition — portion size. Young children should not be expected to eat adult-size portions; this is often the cause of the “clean your plate” fight at the dinner table. Sometimes a child’s appetite just doesn’t match the amount of food they are served.

What is the appropriate serving size for a child? Research suggests that for children aged two to five, taking a one tablespoon per year of age approach is a good rule of thumb. This allows for increasing portion size as children get older.

For example, a two-year-old should be served two tablespoons of chopped chicken, two tablespoons of green beans, and two tablespoons of applesauce. If they eat that and want more, that’s okay. Better that they ask for more rather than being encouraged or forced to eat more.

The study is published in The American Journal of Clinical Nutrition.