Q: I have three boys, ages 2, 4 and 6, and am having problems dealing with the 4-year-old. He is different from my other children and I am confused and worried. He is very sweet, loving, helpful and affectionate. On the other hand, he is lazy, manipulative and unable to entertain himself.

I can do only a little bit about the laziness and I am at a loss as far as getting him to play by himself. I play with him often, but there is a limit. I get him started on things with the hope he can carry on himself. I also provide playmates and preschool.

I am worried about him and his future. Please help.

A: There is no such thing as a lazy child. He may be lonely or tired or afraid or depressed or even a little slow. Or he may be trying to get more attention or have some nagging physical problem. But he's not lazy.

Children have different temperaments, of course, which tend to match their basic shapes. In extreme cases, the ectomorph -- that long, thin, round-shouldered child -- is usually more sensitive, tense and inhibited and he's not very interested in food. The plumper, softer endomorph tends to have a short neck, small hands and feet, loves to eat and is easygoing and friendly. And then there's the solid little mesomorph, with his squared shoulders and all the energy and assertiveness -- and aggression -- to take on the world.

None of these children are designed by nature to be lazy, tired or bored. You have to find out the cause of these symptoms. When you take care of it, your little boy will be able to entertain himself, and he won't be so manipulative either. Right now that's his only defense.

Let's look at the psychological side first. You're dealing with not one son but three -- a very special, joyful and demanding combination for a mother -- and you're obviously doing a good and caring job. Even though this son is a middle child, he's getting his full share of attention.

Loneliness shouldn't be a problem for him either, with an older brother and a younger one, playmates and preschool.

Your child may seem lazy because he's really afraid of failure. But this would only happen if you routinely gave him tasks that were beyond his ability, or if you didn't give him the time, order or instruction to do them well, or if someone in the family regularly mocked his mistakes. This seems unlikely.

He might act lazy because you notice him most when he does nothing. A child chooses the behavior that will get him the greatest attention from his parents, even if the behavior -- and the attention -- is negative.

Spend a whole morning watching him at school. If he's bright and sparkly when he's there, and bored and lazy at home, you'll know you've slipped into this pattern. In that case, you'll have to handle him in a different way -- by ignoring him when he fusses for your time, and by being attentive when he's busy and productive. He'll respond by being more difficult than ever for the first week, but he should come around within a month.

However, if he's listless when you see him at school, and the teacher says he always acts that way, you're probably looking at a physical problem.

A child can be hypoactive for many reasons.

Many mothers, and some doctors, find that diet management is the most effective cure for hypoactivity as well as hyperactivity. Some children simply don't get the right things to eat, or get enough of them. Juice, dry cereal and a few ounces of milk can't give any child enough energy to last until noon, and cookies for a snack will only lower his blood sugar more. See that your son gets a sturdier breakfast, like eggs, French toast or oatmeal, as well as fruit -- which is better for him than juice -- and that he has morning and afternoon snacks of fruit with cheese or peanut butter.

You also should consider food sensitivities, which can cause psychological reactions. Many children are bothered by some of the 3,000 or so additives allowed in our foods, such as dyes and preservatives, and by salicylates, such as aspirin, oranges and tomatoes, and must be put on the Feingold diet. Others react poorly to such foods as milk or wheat. Dr. William G. Crook and Laura Stevens explain such sensitivities in their new book, Solving the Puzzle of Your Hard-to-Raise Child (Knopf, $17.95).

Other children are lethargic and even depressed because their thyroid is low -- which takes a TSH test to prove properly. Or they have hypoglycemia, because they don't process carbohydrates well. Still others have some small, correctable problem that stops them from taking in a particular vitamin or mineral or amino acid, making them anemic or skewing their energy level in other ways.

Keep a daily diary of your son's foods, his stresses and behaviors, and then ask the pediatrician to review his case history and give him a thorough physical. If necessary, he can refer the child to an allergist or endocrinologist at a teaching hospital, or to a child development center for further physical, mental and psychological tests.

There's no point in having your son work at half-capacity when, with the proper diagnosis, he could do as well as nature intended.

Questions may be sent to P.O. Box 15310, Washington, D.C. 20003.