Q: I am a grandmother now, but I reared six children. As a grandmother, I am more objective in assessing behavior problems in the five grandkids I see frequently and am much more objective than I was with my own children.

My youngest daughter, 23, resents any guidance. Naturally, we refrain from any more criticism than necessary for fear of driving her away from us, but I won't let her little boys destroy my house or raise the noise level beyond reasonable limits. Her husband is on a remote assignment to Korea and she and the boys -- 4 and 2 1/2 -- live 120 miles away and visit us every other month.

We're so pleased when they come, and we set aside anything we had planned to make the visit more enjoyable. We try to "spell" her by feeding the boys their breakfast and getting up if we hear them at night. My husband usually gives us an afternoon free of the children to shop or do what we like. I sew for her and the boys, perm her hair and feed them what they like to eat. She appreciates all this and was overwhelmed when we built a sandbox, chalkboards and bean bag games to entertain the children. In short, she is not ungrateful; she was always a joy at home. Our visits would be wonderful if only those little boys could be taught to respect a few simple orders, such as "Wait," "Don't interrupt," and "No!"

The 4-year-old is the John McEnroe of the nursery school set. Because he wants something, he thinks he should get it. He is a nonstop talker (we have learned not to interrupt him when he bursts in to tell a story, because he is like a broken record and just starts over at the beginning again!). While this can be very interesting from a parent's (or grandparent's) point of view, it's impossible to have an adult conversation while he is awake.

He is preoccupied with policemen and "bad guys" (because his father is a military policeman?) and most of his play is oriented to intrusive siren noises, violent car crashes, etc. His sturdy younger brother is the butt of a lot of "accidents" caused by this sort of play. I can't recall these two playing unattended for more than five minutes without one of them wailing.

Why don't they get along better? How can we teach them not to interrupt adults?

A: No age difference is perfect between children, but 18 months is less perfect than most. And for good reason. It means that one child will be 2 1/2 when the other is 4.

As the Gesell Institute reports so eloquently in "Child Behavior" (Harper and Row, $5.95), "the 2 1/2-year-old is not, temperamentally, an easy, adaptable member of any social group." And as for 4, "the key words are out-of-bounds." As you must have blessedly forgotten, a certain amount of this rowdy behavior goes with these ages, and when they reach them simultaneously, their behavior is worse. Each abrades the other.

The violence and the roughhousing is part of the package now but since the older child has been a handful right along, you're looking at a bigger problem. All the visits to loving grandparents haven't melted that extra scoop of sibling rivalry he carries in his heart. And nothing ever really will. Children just can't believe that each one is loved best but for different reasons.

This idea will be easier for them to accept -- at least in your house -- if you and your husband make a few changes. Some of it is in your attitude.

You'll be happier if you pay more attention to your own needs and wishes. If you give up all of your plans every time they visit -- rather than some -- you're going to resent this young family; and if you tell your daughter to correct the boys when you're itching to do it yourself, she's going to resent you.

If something bothers you, take care of it yourself. As long as most of your discipline is preventive, your daughter will be relieved, for, after all, she comes home to be a daughter, not a mother.

When siblings rival, separation is the key. The more the children are apart, the better they will be, because the older one in particular needs individual attention. Your husband can take him to the hardware store while the baby is in the tub and you can have him help you make a pie while his mom takes his little brother to the yard sales.

Nighttime is another good time to visit. A summer walk in their pajamas becomes a star-gazing adventure and a wake-up visit in the middle of the night will awe the 4-year-old, even though he'll fall right back to sleep. To say you love him, and to congratulate him for doing some kind or loving thing that day, will give him sweet dreams and sweeter behavior the next day.

When you reward interruptions with attention, however, you invite more interruptions. Instead, he needs to be told that he must wait his turn, and when he doesn't, put him in the corner for a few minutes, hold his shoulders gently and ignore his squawks.

The same maxim applies at every age: your house, your rules. It's a lesson every child has to learn.

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