The Utah Court of Appeals held there was no reversible error:

The State responds that the prosecutor did not intend to enhance A.C.'s credibility, but merely to establish her competency to testify truthfully. Defendant points out, however, that A.C. was competent to testify without prior qualification. See Utah Code Ann. § 76-5-410 (1995) ("A child victim of sexual abuse under the age of ten is a competent witness and shall be allowed to testify without prior qualification in any judicial proceeding.").

We conclude that, to the extent that the prosecutor improperly intended to enhance A.C.'s credibility, it was error to allow the testimony. Under the circumstances of this case, however, that error would not have been "obvious" to the trial court. ... Although section 76-5-410 abolishes the need to establish competency of certain victims of child sexual abuse, the trial court still retains discretion to exclude the child's testimony for other reasons. See State v. Fulton, 742 P.2d 1208, 1218 (Utah 1987) (stating that trial court may exclude testimony of child witness under Rule 403); see also State v. James, 560 A.2d 426, 432 (Conn. 1989) (concluding that, although state statute declares competence of child sexual assault victims, "courts have authority to exclude evidence that may be more prejudicial than probative").

In addition, even after competency has been established, "counsel may harbor doubts about the jury's confidence in the child's testimonial capacity." John E.B. Myers, The Child Witness: Techniques for Direct Examination, Cross-Examination, and Impeachment, 18 Pac. L.J. 801, 806 (1987). In those circumstances, counsel may "utilize a portion of the direct examination to ask questions designed to demonstrate the child's competence." Id. One factor bearing on competency is the child's "'sense of moral duty to tell the truth.'" ... Evidence of religious beliefs has been used in competency determinations to establish a child witness's moral duty to tell the truth. See [State v. Wilkerson, 612 P.2d 362, 365 (Utah 1980)] (recognizing child's statement that she knew "it was wrong to tell a lie," having learned about it in church); see also Barrett v. State, 744 S.W.2d 741, 744 (Ark. Ct. App. 1988) (approving competency determination in which child witness testified that he understood "that God would punish him if he told a lie"); Jordan v. State, 322 S.E.2d 106, 107 (Ga. Ct. App. 1984) (upholding finding of competency of eight-year-old who testified that she believed in God and knew that she might be punished for lying).

State of Utah v. Hall, 946 P.2d 712 (1997)