Parents today feel that they must raise their children in an environment over which they have little control. The values they would like to instill in their children seem so easily overwhelmed by commercial culture.

Of course children will be vulnerable to their curiosity about obscenities — marketed to them by the media — that their parents forbid. Should we act surprised, though, at a child's first foul word? Could they possibly understand what they are saying? How should we respond?

Children first hear "dirty words" at 3 or 4; their understanding of language at these ages is sophisticated enough for them to take note of the special intonations and contexts associated with such words. But if they are to understand what is different about dirty words, they need to experiment, to try them out.

No one takes the more innocent ones too seriously: "Mommy, you're a poo-poo face." "Daddy is a fat bum-bum." At most, each parent reacts with a cringe, then a laugh. "Where did you hear that?" "From you."

Parents are usually not satisfied with that, even when it's true. They wonder: "Whom did he play with yesterday? Did he learn it from him, or did he hear it on that television show?"

Parents do need to be concerned because they must teach their children about language, its uses and its power. Their job is to model behavior and create an environment in which children can learn how their words and actions affect others.

Parental work is harder than ever as offensive sexual talk (not all talk about sex need be) becomes ubiquitous on television, radio and the Internet. But overreactions just make the searing and dirty words more intriguing to children and give the words a power they will want to try out.

Why do parents overreact? A child who swears challenges a parent's desire for him to fit in and please others. Dirty words may seem like a sign that parents are losing control as their child grows up; they may appear to signify loss of innocence — so hard for parents to face. They may seem to imply that more frightening behaviors are to come.

Already parents have fears about how a child will fare in a dangerous world. It may frighten them to see their child so vulnerable to imitating peers. Everyone in the family is afraid it will get worse.

Kids from down the street may become models as a young child imitates their dirty words and brings them home to try out on parents. Sexual curiosity and four-letter words are right around the corner.

A child's way to discover the limits of a taboo is by testing his parents over and over after an initial overreaction. Innocence has now turned into outright provocative behavior. A parent worries: "Will he use it in public? What does it mean? Could he have been molested?" All these fears may run through parents' minds as they respond: "We don't say words like that! We don't swear in this family!"

But often it's not that simple. Parents who sometimes say swear words themselves may now wish they hadn't. How confusing for a child to understand that what comes out of his mouth is treated differently.

Instead of being offended when a child swears, a parent might try to discover the reason for it. When you can damp down your response, the offensive words will begin to lose their interest and you will hear them less often.

If your child uses them too freely in public, use such an incident as a teaching opportunity: "When you say these words, people are upset. Those are words we don't say unless we want to bother other people. Is that what you mean to do — or does it just slip out?" In saying this, you are attempting to place your negative view of swearing and dirty words in context — that of sensitivity to others' feelings.

In the relative hierarchy of offensive behavior, swearing is more innocuous than most, especially if ignored, and thereby eventually extinguished. Children aren't likely to become chronically foul-mouthed in an environment that doesn't value swearing and dirty words.

Questions or comments should be addressed to Dr. T. Berry Brazelton and Dr. Joshua Sparrow, care of The New York Times Syndication Sales Corp., 609 Greenwich St., 6th Floor, New York, NY 10014-3610. Questions may also be sent by e-mail to: Questions of general interest will be answered in this column. Drs. Brazelton and Sparrow regret that unpublished letters cannot be answered individually. Responses to questions are not intended to constitute or to take the place of medical or psychiatric evaluation, diagnosis or treatment. If you have a question about your child's health or well-being, consult your child's health-care provider. Distributed by New York Times Special Features