Is evidence ever needed? Outside of the testimony of the victim, not that that can really be called evidence. And it's not constrained to children either - I've come across a lot of new stories about men who were later exonerated of raping women, after spending a lot of time in prison. Where the women came out later and admitted they made everything up. I'm not sure if I would feel comfortable alone with a woman, at least if I was in a position of power above them like their boss or teacher etc., without a recording device on.