I'm not sure that the CPS should be pilloried too much in this case. When the child involved has made such a serious allegation to the Police, it must be incumbent on the CPS to consider whether a charge should be made.
Due to the strict reporting restrictions imposed by the Judge, not all of the court proceedings have been made public, and never will. In order not to identify the child, most of La Vell's testimony was not reported. But there would appear to be no other evidence, such as forensic or independent identification which could be used in court.
So in the end, it came down to whether the evidence given by the child in court could be relied on and believed by the Jury. The onus is on the prosecution to prove their case, not for the defendant to prove his innocence. Its often the case that to throw doubt on the prosecution case, the defendant is best advised to take the witness stand.