And there's also the matter of the defendant's right to be confronted by the witnesses against him. The Child Hearsay Rule has been enacted in many states to sidestep this, but in some jurisdictions the victim still has to take the stand. And, again, many jurors want to hear from the victim before they'll convict.
You can never predict how an appeals court is going to rule, but it seems to me that allowing the dog in the witness box is along the lines of allowing the victim to testify behind a screen so she doesn't have to look at the perp, or allowing her mama or sister to sit next to her -- especially with children, the trial judge has a lot of discretion in controlling his courtroom and directing the examination of witnesses. At least he does around here.