I KNOW A GUY who was a prosecutor and whose brother went to jail. I know this to be a fact, although I know, too, that it sounds like a Pat O'Brien movie in which one brother becomes a priest and the other becomes a hood. There have to be times, after all, when the cliche is true and art really does imitate life.

The only difference between the movie families and the Wilson family of Pasadena, Calif., is that the Wilsons have produced no priests or prosecutors. In fact, they seem to have produced nothing but criminals and prostitutes and in the course of time, some children. The authorities have taken them away.

Wilson, of course, is not the real name of the family. That is a secret to protect the identities of the children. What is real, though, is the situation and it is, in a word, scary. There are, at the moment, three unmarried Wilson sisters who are the mothers of the four children who range in age from 18 months to 10 years. All of the mothers have been arrested for prostitution as has one of the grandmothers.

As for the fathers, they all are in state prison. So are most of the other close relatives. In fact, court records say that 15 of the closest relatives have been arrested a total of more than 400 times on charges ranging from petty theft to murder and two of the children, an 8-year-old and a 9-year-old, already have been arrested for shoplifting. The kids seem destined to go into the family business.

It is for this reason that the authorities have taken the children away from the family. They point out, with a certain amount of logic, that the kids are bound to follow in the parents' footsteps, that crime breeds crime, and that the state has an obligation to save the children from that sort of life. They cite that most undefinable of all standards -- the good of the child.

They undoubtedly have something there. Common sense tells you that children raised among thieves and prostitutes will, as day follows night, become thieves or prostitutes themselves. We all recognize that there are such things as role models and the ones that these kids have are not socially acceptable -- so much so that even the undisputed love their mothers have for their children might not compensate: "I carried that baby for nine months," said one of the mothers. "I had labor for that baby. I've stolen for that baby. I've gone to jail for that baby. I've gone through changes for that baby. You can't take him away from me."

The standard of what is best for the child can be the most slippery standard of all. It has been invoked in Chicago to take a boy away from a couple who wanted to return to the Soviet Union. That was essentially a political decision -- a finding that one political system (ours) is better than another political system (theirs) and that the child would be better off remaining here.

When it comes to the Wilson kids, though, political views are not an issue and it is, for that reason, a quite different case. Still, what is at bottom here is not a finding that the kids were unloved or abused or even that their mothers are hardened criminals (they are not in jail, after all), but rather that they are social misfits. They are prostitutes and neither the courts nor society approves of that. No argument there.

But you can worry about the precedent and question whether society has some legal right to impose a uniform moral standard on families. What, for instance, if some court decides that a family is unfit to have children because of weird religious practices -- as weird, say, as the ones that resulted in the carnage at Jonestown? What if a court made a similar finding because both parents were Nazis and were raising their children to hate?

No one writing in Washington can possibly say what should be done about kids in California -- or anywhere else for that matter. The court probably did the right thing, but its decision makes you want to wish also for some declaration in reaffirming the role of the family, some ringing pronouncement that this case is unique and represents no precedent at all -- some admission that we still don't know much about mothers and kids and love and how it all interacts. After all, there was an essential truth to those Pat O'Brien films. Life remains, as always, a mystery.