maddyone, the latest research in the UK in 2017 reported 4% of all allegations made to police were found to be false. Research throughout Europe and North America concludes between 2% and 6%.
The police and CPS only take a case to trial if they are 85% certain of a successful prosecution. That excludes children under the age of 7, who are rarely seen as appropriate witnesses, not least because of the possible damage to the child who will face fierce cross examination, clever questions designed to trip them up, confuse them. If there are multiple alleged perpetrators, the child can face that kind of cross examination from several barristers. That's what happened in the various child sexual exploitation trials reported on recently.