The Supreme Court of Pennsylvania has held that in a child sexual abuse case expert testimony as to the veracity of a class of children of which the victim-witness is a member, is an improper invasion of the jury's function of assessing the credibility of a witness.
Commonwealth v. Seese, 512 Pa. 439, 517 A.2d 920 (1986).
Helen A. Nicholas,
Criminal Law - Child Sexual Abuse - Expert Testimony as to Credibility,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol26/iss4/9