The issue of the credibility of a child's or adolescent's testimony in judicial sexual allegations has already been developed in many articles and books of the scientific literature. This article reports on the expert practices in the field of child psychology and legal psychiatry for credibility expertise in Switzerland. After illustrating the issues at stake in the analysis of various testimonies in the context of a recent trial (the Outreau case), we will describe the Statement Validity Analysis, a credibility assessment methodology recognized by the scientific literature and Swiss case law.