The poignant scene is played out time and again in America's courtrooms. A small, bewildered child sits in a witness chair, being led by an attorney through shocking testimony. The youngster speaks haltingly of unspeakable things done to him or her by a stranger, a baby-sitter or even a parent. Could such an innocent soul possibly be telling anything but the truth?

Most legal experts, child psychiatrists -- and juries -- have long thought that children rarely lie about sex-abuse crimes on the witness stand. On the strength of that assumption, many adults have been sent to jail for sexual abuse or other charges, professing all the way that they are not guilty. But evidence is mounting that children, particularly those who have been extensively coached, give inaccurate testimony far more often than previously imagined. Both research studies and courtroom experience are causing many psychiatrists to question their views of the reliability of what comes from the mouths of babes.

A stunning piece of evidence came late last year when a California appeals court overturned the convictions of three men and four women for molesting 10 children. The adults had maintained their innocence but were sentenced to a combined total of 2,619 years in prison. The case fell apart, and the adults were freed when three of the children later recanted their testimony and the state attorney general's office criticized the way prosecutors had allegedly manipulated the children's testimony.

Recent research has shown how easy it is for youngsters to stray unwittingly from the truth. Psychologists Karen Saywitz of Harbor-UCLA Medical Center and Gail Goodman of the State University of New York at Buffalo interviewed 72 girls, ages 5 and 7, about routine medical procedures they had received. Half were given full examinations, including anal and vaginal checks, and the rest were given just general physicals. When the first group was asked a broad question about what had happened, only eight mentioned the vaginal examinations, and when the children were shown anatomically correct dolls, six pointed to the vaginal area. But of the girls who received only a general checkup, three claimed they had also had vaginal or anal exams. One child even reported that "the doctor did it with a stick."

Child-custody disputes are often the trigger for youngsters' unwitting lies. Suspicions can cause parents to launch what legal scholar Douglas Besharov of Washington's American Enterprise Institute calls "the atomic bomb of child- custody fights, the charge of sex abuse." In these stressful situations, children quickly discover what adults want to hear and can offer lies or distortions in order to please an anxious parent or social worker. A study conducted by the American Academy of Child Psychiatry found that in custody disputes involving charges of sex abuse, as many as 36% of the allegations were later proved to be untrue.

Research by psychologist Alison Clarke-Stewart of the University of California at Irvine illustrates how easily adults can sway children's perceptions. In that study 75 five- and six-year-old children were asked to % watch a man clean up a room. During that time, he picked up and cleaned a doll. Later an interviewer told the children she thought the man had been playing with the doll. When first questioned, 25% of the kids said the man had played with the doll, and the rest said he had cleaned it. The interviewer then told the children she was certain that the man had been playing with, not cleaning, the doll. In the end, all but two children accepted the interviewer's story as the truth.

Misleading questions by adults can cause children not just to lie but also to believe their falsehoods. Besharov cites the case of a three-year-old who told a social worker a story about a piece of candy being dropped into her underpants. After interviews by various child-protection workers, the story evolved into a tale that a candle had been inserted into the child's vagina. It took months of further interviews to discover that the original story had been correct.

The current methods for obtaining evidence in sex-abuse cases -- direct questioning and the use of dolls with sex organs -- are under fire. "Kids can be fed ideas they quickly come to believe are true, and these dolls are highly suggestive," says Lenore Terr, a professor of psychology at the University of California at San Francisco. For example, some of the dolls lack hands and have only painted eyes, yet they have highly explicit genital areas. Terr stresses that normally inquisitive children who play with these dolls can mistakenly be suspected of having been abused.

The controversy is sure to escalate this spring, when the American Psychological Association publishes a book called The Suggestibility of Children's Recollections, in which several experts question the truthfulness of kids' testimony. The A.P.A. will not allow outsiders an advance look, but a psychologist involved in the project says the book shows that "there are definite limits to our knowledge about whether children are telling the truth."

What these researchers and others are finding is that truth for a child can be blurred, especially in periods of stress, such as during a trial. To protect children from sex crimes -- and adults from unfounded accusations -- child-welfare workers and prosecutors will have to take special care when searching for the truth.