Applicable federal or state law determines who is a "child" for purposes of Federal Rule of Evidence or comparable state rules that authorize the use of other instances of child molestation or child sex abuse against criminal defendants who are on trial for child molestation or child sexual abuse.

Cf. Mobil Exploration & Producing U.S. Inc. v. Cajun Construction Services, Inc., 45 F.3d 96, 99 (5th Cir. 1995) (holding, in an action for recovery of money, that the district court erred in refusing to consider plaintiff's evidence of defendant's routine practice for loading its trucks because...The routine practice of an organization is admissible under Federal Rule of Evidence 406 or a comparable State rule in order to show conduct on a particular occasion even if the routine organizational practice is volitional.

Doe v. Glanzer, 232 F.3d 1258, 1269 (9th Cir. 2000) (upholding trial court's exclusion of accused's prior sexual misconduct because, even though such evidence was relevant, it was unduly prejudicial to the accused as the events were dissimilar and there was significant time lapse between the incidents ).Federal Rule of Evidence 415 and comparable rules in some states create an exception to the prohibition against "circumstantial" character evidence, the prohibition in Federal Rule against the use of character to show conduct. Rules such as Rule 415 provide that in a civil action which a claim rests on a party's alleged conduct constituting a criminal sexual assault or child molestation, evidence of that party's commission of another offense or offenses of sexual assault or child molestation is relevant and admissible.

United States v. Bruguier, 161 F.3d 1145, 1148-1150 (8th Cir. 1998) (upholding trial court's ruling that allowed the government to cross-examine accused's opinion character evidence witnesses concerning whether they knew about specific incident, in order to explore the witnesses' bases for holding their...If a criminal defendant offers evidence of his or her character circumstantially - to show he or she did not commit the crime charged -- the prosecution can offer rebutting evidence of defendant's character.