Q. I have a grandson who is 4 years old and already has a weight problem (almost 70 pounds). This has him very upset. At this young age, he wants to go on a diet because he wants to be like other children.

He is a very good-looking child (42 1/2" tall), but it is difficult to buy clothes for him. We are very concerned that his unhappiness with his weight will end up harming him. Do you have any suggestions about what we can do to help him?

A. There is probably nothing that embarrasses a child more than feeling awkward and nothing makes him feel quite so awkward as being overweight. And a child who is 3 1/2 feet tall and weighs almost 70 pounds is definitely overweight.

Dr. Lawrence D'Angelo, an expert in eating disorders at Children's Hospital National Medical Center, says that the average 4-year-old weighs almost 40 pounds, which means that your grandson has almost doubled his proper weight. This puts his health in jeopardy; 80 percent of overweight children become overweight adults.same diet he does, whether they're overweight or not, and will eat slowly at regular mealtimes, seated at the dining-room or kitchen table. Movable feasts are the way to fatdom.

A child is bound to beg for treats that others have and there is sure to be a visitor or a sitter (if not a parent) who'll give them, at least some of the time. Most temptation can be avoided in silence, by getting rid of fattening or unnecessary foods.

Give away or throw away the bacon and sausage; pizza and pasta; cold cuts and hot dogs; nuts and peanut butter; cookies and cupcakes; crackers and chips; candy and ice cream; sour cream and whipping cream, syrups, jams and jellies.

Fats should be limited severely. As someone once said, inside every fat child is an even fatter child trying to get out. Butter only greases the way.

His parents may have to make other basic changes so that the food he eats is more filling and nutritious. Oatmeal and grits are better than dry cereal; fresh fruit is better than fruit juice or dried fruit and

You can see how it's already affecting his happiness, and this will get much worse in elementary school, when conformity means so much.

The first step is a consultation with a board-certified pediatrician and then perhaps an endocrinologist, to see if he needs thyroid or other treatment. But if overeating has caused the weight gain, refined carbohydrates -- junk foods -- are usually the reason. It only takes an extra 3,500 calories to turn into a pound of flesh.

Since exercise burns calories, your grandson needs regular work-outs. Swimming is about the best because he'll use so many muscles. He'll also feel less conspicuous in the water; his buoyancy will help him move easily and he'll have a good time. Find an indoor pool so he can swim year-round.

The rest of his success depends on how well he follows the doctor's diet. While your grandson shouldn't be expected to lose weight -- this could hurt his general growth -- his diet should keep him from gaining a pound more, so that he grows into his weight. By age 7 he will be down to the 95th percentile -- a medically acceptable level -- and by 9 he should be about average.

This can be done, so long as his parents -- and his grandparents -- show their love by saying no when he cannot. He needs the whole family to care enough that they will follow, without complaint, the rough, whole wheat bread is an improvement over white.

Since milk and cheese are both nutritious and fattening, the doctor will probably require a switch to skim milk and low-fat yogurt or cottage cheese. The cooking in the child's home also should change. Foods should be boiled, steamed, baked or braised, not fried, and sauces, gravies and desserts must be forgotten. Chicken and fish should be served (without skin) as often as possible, in place of the more fattening red meat.

The better a meal is planned, the more successful your grandson will be. You might suggest to his parents "The Shoebox Diet":

Pack and refrigerate a shoebox each night, filled with his food allotment for the next day -- real food when possible, with tickets good for stew or soup. This gives a child, who can't understand anything as abstract as a calorie, the concrete examples to help him stay on a diet.

There will be some fussing, of course. Have you ever known a dieter who didn't fuss? And being 4, he will have to eat many foods he doesn't like, but being an eater by nature, he'll do it, rather than go hungry.

All of this will help him hold his weight and win him an occasional, non-edible reward: a toy or a new and smaller belt.

A cupcake will never seem as sweet.