A new study found an effective way to encourage children to pick healthier meals for lunch - labeling the foods with smiley faces.

If the smiley faces weren't enough of an incentive, a small prize sure was.

Researchers devised two efforts in an attempt to curb childhood obesity. They focused their study in a cafeteria at a Cincinnati school involving kindergarteners to sixth-graders.

The researchers placed green smiley faces on the healthy food, including fruits, vegetables, plain white fat-free milk and an entrée with whole grains. Three months later, they introduced the "Power Plate" containing four healthy foods. Those who chose the healthy plate were given small prizes, such as a sticker, temporary tattoo or mini beach ball.

After the five-month study period, the findings showed that the smiley face and power plate encouraged 48 percent of the students, up from seven percent, to buy milk. Those who were buying chocolate milk were cut in half. Fruit and vegetable purchases, on the other hand, increased by 20 percent and 62 percent, respectively.

Researchers concluded that smileys and rewards are effective and cost-efficient ways to promote healthy eating in students.

"It looks like we found a very promising, low-cost and effective way of improving the nutrition of elementary school children," Robert Siegel, study author and medical director of the Center for Better Health and Nutrition of the Heart Institute at Cincinnati Children's Hospital Medical Center, said in a press release. "This type of program may be a useful component in schools trying to improve the nutrition and health of their students."

The study was presented on April 26 at the Pediatric Academic Societies (PAS) annual meeting in San Diego.