Mentally fit person with sufficient understanding of the circumstances. While, commonly, there is no minimum age limit, a judge may decide whether a child’s evidence can be allowed. In civil cases, for example, a child too young to comprehend the solemn nature of an oath is considered unsuitable as a witness. In criminal cases, however, the testimony of a child may be allowed as unsworn evidence. In most cases, the spouse of the accused is considered a competent witness for the prosecution.