"As we were driving along the outer loop of the Beltway at about 7 p.m.," writes Jane Brown of Severn, Md., "something was thrown against wour car. It happened as we were in front of the apartment development that sits off the Beltway just before you hit the Baltimore-Washington Parkway exit.

"My husband didn't stop. He said it was probably a snowball and there was little chance we would catch the person who threw it. When we got home, we found a hole in the front of our grill about the size of a fist. There was a rock wedged in it.

"We called the Maryland State Police. They told us we were lucky. Two other motorists before us had lost their windshields. The police also said this was the third night running for this activity.

"The police planted an unmarked car in the area last night. Nothing happened, so the car left. As soon as it was gone, the activity begaan again.

"All of this makes one wonder what parents are doing with their kids these days. The rock throwing takes place well after dark. Do the parents know where their children go night after night? Don't these parents realize they are legally responsible for the actions of their children? Something needs to be done to show parents and children alike that this kind of activity threatens life and limb and cannot be looked upon as a childish prank."

Yes. But what can we say or do that hasn't already been said and done?

Even the throwing of relatively soft snowballs is not a childish prank. A startled driver can lose control of his car. The snowball can find a partially open window and hit the driver in the face. Injury and even death can result. There is nothing funny or prankish about this type of activity.

I would not stop with your question about whether these parents know where their children ar at night. I would go on to wonder whether the parents know, or care, what their children are doing.

We can't keep our children locked up day and night, and as they grow older we must accord them increasing opportunity to move about and explore. So it's just not practical to think in terms of constant physical control and/or supervision.

The important thing, I think, is to give the child constant instruction in what is good and bad, wise and foolish, civilized and savage, so that we won't have to know where he is or wonder what he's doing. At every opportunity the parent must teach and preach, yet find ways of doing it within the child's attention span and capacity for accepting instruction. If we do our job right, we will never have to worry about where our children are or what they are doing.

The problem these days is that TV, comics, news reports, the theater and popular music all exploits kinky conduct and encourage immature young people to engage in it. The parent who succeeds in inoculating his child against these poisons earns the Good Parent Award: gray hair. But he has something to show for it.