Q: I would like to address a concern we as grandparents have regarding the language development of our only grandchild. She is 2 1/2.

Our daughter is a college graduate who married a man with lesser education and is living in a small, almost rural area in the southwestern part of our state. When we visit, it seems everyone we meet uses "ain't" in their vocabulary, including family members, baby sitters and the child's friends.

Our daughter is distraught over this and has made many attempts to correct her little girl. She repeats the sentence back to the child, using "isn't" instead, but to no avail.

In addition, the child is using incorrect verb tenses, which she hears constantly.

Along a similar vein, how little or how much should one respond and react when a child tries out a four-letter word? I know most parents are confronted with this at some time.

A: There are three issues here and one is much more serious than the others. Let's get rid of the lesser ones first, starting with foul language.

Four-letter words are common among children, and if they try them out at home, a parent swiftly and seriously explains that no child may talk like that in her house. When her child does it again (and she will), she's stood in the corner without any lecture but with adult hands to hold her gently in place for a few minutes while she wails. And that's that. There should be no dwelling on the subject. Young callers who come cussing are simply asked to use good language so they can be invited back again.

This won't make the foul language go away completely -- particularly at the ages of 4 and 7, and certainly 11 and 12 -- but usually it will make the child discreet enough to let her parents ignore her occasional lapses, most of the time.

As for your granddaughter's grammatical mistakes -- they are almost irrelevant. A toddler bumps into the language as much as she bumps into the furniture -- a lot.

It won't help if your daughter corrects her frequently, especially at 2 1/2, because it doesn't help much to correct a 2 1/2-year-old about anything. She's too busy learning the ABCs of independence to bow to anyone. Moreover, her mother's constant corrections will only imprint the "ain'ts" more strongly.

Instead, your daughter should handle this problem indirectly. Tell her to praise success, ignore mistakes and set a good example, just as she deals with all toddlerhood problems that can't be solved with body English.

In time, your granddaughter will be more grammatical around her grandparents and her mother -- because she knows you all like it -- and will improve still more when she starts school. Reading, writing and good marks all reinforce good English.

However, she will still say "ain't" and use wrong tenses when she's with children or relatives who talk like that, because the language will seem appropriate then. This is much the same as the child who speaks black English or Yiddish in her neighborhood and shifts to standard English when she's in a broader setting. In a way, your granddaughter is growing up in a bilingual situation -- but it's hard for her mother to like the country language since it isn't quite as acceptable as say, Parisian French.

This may reflect a problem much more serious than grammar. Your daughter must feel like she's losing her child to her husband's alien world. This can lead to tension in the marriage, for cultural differences of language and manners and customs can rip couples apart more effectively than personal ones.

A partner may get embarrassed or annoyed because he or she doesn't understand what the other really means. What is acceptable to one person may make the other uncomfortable. These differences may be disguised for years, only to bloom when a child is involved.

You can do a great deal to smooth the problem by reminding your daughter that her little girl needs happily married parents much more than she needs lessons in good grammar. She also needs many loving relatives from both sides of the family, and it simply doesn't matter if their word usage is poor. As long as their values are sound, their kindnesses will more than offset their mistakes.

You also want to help your daughter appreciate her country home so her child will do the same. For a warm, rich, eye-opening view of their part of the country, you'll both profit by the splendid new Katherine Paterson book, Come Sing, Jimmy Jo (Dutton, $12.95). Although this novel is written for pre-teens and young teen-agers, its universality reminds us that the worth of our neighbors matters far more than their ways.