"Don't play with your food," your father says as you push your peas around on your plate. Have you often heard someone saying that?

For kids in about 500 schools in the midwestern United States, these words mean something different. Playing with food is part of their homework. It's not real food, though. The food is part of a card game called "Betting on Bulk." The front of each card in this game shows a color picture of a food like pickles or peas. On the back, different symbols let the player know how good the food is for them. When you play games with the cards, the person with the most nutritious food wins.

Did you know that one sweet pickle contains iron and vitamin C? That's pretty good -- but not as good as peas. A half cup of peas contains vitamin A, three forms of vitamin B, vitamin C, iron and protein. The peas win!

Why do peas beat pickles? They have a powerful combination of vitamins, minerals and protein. Vitamin A helps keep your throat healthy. Vitamin B helps unlock energy in the food you eat. Vitamin C helps heal cuts. Protein builds muscles. And peas have one more winning ingredient: fiber. Fiber is a natural substance found in many fresh foods which helps keep your digestive system running smoothly.

Foods high in fiber are also likely to be highly nutritious, which means they're good for you. There's a symbol for fiber on the back of the "peas" card. It's a strong-looking creature dressed in jogging shorts, called "The Incredible Bulk."

If you draw a card with raisins on the front, you'll find out that raisins have iron and fiber in them. The peanuts card shows that they contain fiber, vitamin B, iron and protein. Both nuts and raisins are nutritious.

But turn over the cola picture, and you see a practically blank card. The only symbol on it is a smile standing for "tastes good." The nutrient and fiber spaces are empty. Cola isn't nutritious.

These are the kinds of things kids enrolled in the "ABC's of Nutrition Education" classes learn. The course was designed at Kansas State University by nutritionists, people who are food experts. Researchers there found that most students "moaned and groaned" if they had to learn about food. So the teachers designed a new, fun way to learn. The card game described above is one part of it. For younger children, the researchers designed soft toys. The toys look like different kinds of foods. Each toy has a pocket with a symbol of its most important vitamin stuck inside. The soft strawberry's pocket hides a vitamin C symbol, for example. A squishy milk carton holds the symbol for calcium, a substance needed to grow strong bones.

The games and toys are designed to teach students that fresh foods are often the most healthful. Many of the foods you can buy in a store have been processed or refined. Often these foods will be enriched -- which means that they have vitamins and minerals added to them after they're processed -- but even so they still aren't quite as good as fresh.

"Enrichment returns some vitamins and iron, but fiber and other nutrients are not replaced," says Eunice Bassler, who developed the "ABC's" program. "In this course, students learn that the fiber content of food is one indicator of its nutritional quality."

In the course, kids also learn to put foods in three groups. Anytime foods, like peanuts and peaches, have four or more nutrients, lots of fiber and taste good. Sometimes foods, like hot dogs and ice cream, taste good and have four or more nutrients or lots of fiber. Fewtimes foods, like cola and brownies, taste good but are low in both nutrients and fiber.

People who choose anytime food often, sometimes food occasionally, and hardly ever snack on fewtimes food eat the healthiest diets. Tips for Parents

More detailed information about curriculum for "The ABC's of Nutrition Education" can be obtained from the Department of Foods and Nutrition, College of Home Economics, Kansas State University, Manhattan, Kan. 66506. Programs are available for students from preschool through high school.

From the same address, you can order a $20 kit to make six educational, easy-to-see soft toys -- fabric, instructions and nutrient symbols included.