Q. We chose to live in a culturally and ethnically mixed neighborhood and send our 8-year-old son to the public school, partly to give him a diverse set of friends.

He gets a lot of invitations to visit the homes of classmates and sometimes to spend the night, but we usually don't know the parents personally. Although we of course call and check out the arrangements, the discussions are complicated by expectations and assumptions, as well as different native tongues. With this diversity, we can't assume that other parents have the same rules, values and customs that we do (nor can they assume that we have their rules).

Consequently we have encountered problems. Some parents have guns in the house or they use alcohol, or they don't make the children wear seat belts in the car or they leave them alone for short periods of time or let them watch R-rated videotapes.

I'm concerned about these issues, but I don't want to offend people and interrogate them about their personal habits. How would you approach an initial invitation for a visit?

I could say, "It's important to us that our son use a seat belt, and that he doesn't watch R movies or handle guns, etc.," but I cannot even anticipate some of the situations that might occur. How can we be responsible parents, without laying on rules?

A. If you want to be responsible parents, you have to lay on rules. A child is never too young to learn that there can be many customs but only one basic set of values.

And that's the heart of this issue. Parents who are casual about the routine aspects of child care, such as seat belts and supervision, may be pretty casual about values too.

It's time to examine your own and stand up for them.

Even though friends are terribly important at 8, your son doesn't have to be the most popular boy in the class and he doesn't have to accept every invitation that comes along. It's good to expose him to a cross section of humanity, but he shouldn't accept -- or reject -- children because they come from a different race or nationality.

Teach your son to look beyond the often intriguing cultural differences to find the real substance in people instead. You want him to make a few good buddies who enjoy the same activities, laugh at the same jokes and say no to the same temptations: the kind of people he -- and you -- can trust.

Your son will define himself better -- and find these new friends quicker -- if you get to know the most responsible people in the neighborhood, so they can steer you toward the most responsible parents.

You're not looking for families that are clones of your own, of course, but for ones that take parental responsibilities as seriously as you do. You'll find them in your civic association, your church, the Friends group at your library, and particularly in the PTA.

A few months as a room mother will teach you more about the parents of your son's classmates than any quiz you could give them, and it will be more tactful too. Most people wouldn't take kindly to it if you told them that your son couldn't play with guns or see sexy movies at their house, since most people don't offer guns or sexy movies to their children.

A little more caution would prevent many problems, however. Unless your son is invited to a well-supervised birthday party, it would be better if you only let him visit the children you know fairly well and had him invite the others to play at his house instead. This will give you the chance to talk to them and to see how these children really behave. They probably won't be nearly as bad as you thought -- if you're used to 8-year-old boys -- but if they do get out of hand, remember: Only one level of behavior should apply in your house, even if the other children come from a different ethnic or cultural background. If you let inappropriate behavior go by, you would be telling your son that these children weren't his equal -- an invitation to bigotry later.

Above all, you have to teach your son to carry the family standards with him when he leaves home, because he's sure to find himself in dicey situations sometimes. These standards will give him the excuse -- and the right -- to say no to an R-rated movie now and to more serious temptations later.

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