Tomorrow, if the weather is nice, you may play outside until your parents call you in to your Thanksgiving feast. You will be hungry from running around in the November cold. If you've been thinking about the meal your family is preparing, your imagination will probably have helped you work up an appetite, too.

When you walk into the house, you'll smell the food -- and your body will immediately start working. When the sight and smell of all that good food hits you, special glands in your mouth start producing saliva. That's when you say say, "The food looks so good that my mouth is watering."

Your saliva will come in handy when you start eating the turkey, stuffing, potatoes and vegetables on your plate. When you take your first bite, you begin a process called digestion. Digestion breaks down the food you eat into parts small enough for the cells in your body to use for fuel.

Before your body can use it, your bite of turkey has to be chewed up. Your teeth are specially designed to do this. Some of them are sharp and pointed for cutting. Others are designed for grinding. As you chew, your saliva mixes with the food. It makes the food moist and slippery so that it will move down your throat comfortably. At the same time, enzymes found in saliva start changing the turkey, breaking it into substances your cells can absorb.

The next step is swallowing. Your tongue, which is very muscular, squeezes the food into a wad, and pushes it toward the back of your mouth. From there it passes into the esophagus. The food doesn't just fall into the esophagus like a penny into a well, however. Strong muscles squeeze it down toward your stomach. You don't need to think about these muscles to move them; they work automatically. They're powerful enough to move food to your stomach even if you're standing on your head.

In your stomach, your bite of turkey gets a bath in strong liquids called gastric juices. Your stomach's muscular walls churn these juices with the food, mixing it up into a creamy liquid. At this point, the food you swallowed is not really recognizable as turkey anymore. But it's almost ready to start being useful to your cells.

The next stop on the digestive tract is your small intestine. This twisting and turning tube isn't small at all. If you stretched it out, it would be several times taller than you are. The most important part of the digestive process happens here. A dense lining of tiny finger-shaped bumps covers the inside of the small intestine. You have about 5 million of these bumps, which are called villi. They form a shaggy lining in your intestines.

As the churned-up food moves through, the villi soak up the useful parts and transfer them into your blood. The blood delivers the fuel to every single cell in your body, which keeps you moving and growing.

But not all of the food you eat can be used. Some of it passes on into the large intestine. The large intestine is about five feet long, but it has a larger opening than the small intestine does. This large opening gives it its name. The walls of the large intestine soak up water from your food, and return it to your body. The solid, useless parts of your food pass out of your large intestine when you go to the bathroom.

Some parts of the digestion process are fast. You chew your food for only a few seconds, and the esophagus moves it to the stomach in a few seconds more. The stomach churns your meal for several hours before it turns it over to your small intestine, where it may take as long as eight hours getting through. A meal takes somewhere between 12 and 15 hours to go through the whole digestive system. So if you eat your Thanksgiving turkey tomorrow evening, it will be delivering fuel to your cells around the time you get out of bed Friday morning.

A Thanksgiving meal provides very useful fuel. The protein in the turkey helps build cells. Protein forms about three quarters of the solid parts of you, like skin, hair, bones and muscles.

The carbohydrates in your potatoes and bread provide energy to keep your body moving.

Calcuim, a mineral in the milk you drink, helps keep your teeth strong.

Your vegetables provide vitamins to keep your body chemistry balanced, and bulk to keep your digestive tract working smoothly.

And if you eat a piece of pumpkin pie, you get a rich helping of vitamin A. Orange vegetables like squash and pumpkin contain carotene, a substance which gives them their bright color. In your body, carotene changes to vitamin A. Vitamin A helps your eyes see at night, and contributes to healthy skin and bones.

When you wake up Friday morning full of energy and health, you'll have one more thing to be thankful for -- the good job your digestive system did with your Thanksgiving meal. Tips for Parents

If you're planning an ambitious Thanksgiving feast, including making pumpkin pie from scratch, here's a recipe to get your kids involved in the preparation. It appears in "Creative Food Experiences for Children" by Mary T. Goodwin and Gerry Pollen, published by the Center for Science in the Public Interest, 1501 16th St. NW, Washington, D.C. 20036. Toasted Pumpkin Seeds

Empty the pulp from a pumpkin. Place pulp and seeds in a colander, and rinse the pulp from the seeds. Put the seeds on a cookie sheet, sprinkle them with corn oil and roast at 350 degrees for half an hour. Try these as an hors d'oeuvre.