Not only will the child appear credible when they talk about imaginary persons, they have been led and reinforced to believe in them. The same process can and does happen in regards to abuse allegations. There are no behaviors that are indicative of sexual abuse. In fact, several proponents of Behavioral Indicators have now reversed their views. The difference between Credibility vs. Reliability is, credibility deals with whether the person appears competent to testify.
Reliability deals with whether the person's statements can be relied upon as being factual.
A child witness can appear credible in their testimony, yet their statements may not be reliable because their statements have been tainted by outside sources such as the investigators, therapists, and so on. A child could appear credible when they testify to the existence of the Tooth Fairy, yet we know the statement is not reliable. The same can and does happen in child abuse cases. A defendant can have an expert testify as to the proper protocol for interviewing alleged child victims regarding their abuse. 3d Series, pg.