The following excerpt is from U.S. v. Chavez, 895 F.2d 1418 (9th Cir. 1989):
There is "no precise age" at which a child becomes competent to testify, Wheeler v. United States, 159 U.S. 523 (1895), and factors to consider include the child's intelligence, understanding of the difference between truth and lies, and appreciation of the duty to tell the truth. Id. Other intangible factors that a court might examine are the child's capacity to observe, recollect, and communicate. Pocatello, 394 F.2d at 117.
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