The BBC would have to have taken reasonable precautions if they suspect child abuse, that need only be ensuring the young person was not left alone with the 'suspect'.

They wouldn't necessarily have complete liability.

As for reporting a crime, it could be held that the BBC or it's employees were in a position where they did have a duty to do so though mere suspicion is unlikely to be sufficient, misprision nowadays can still apply to those in certain positions such as school teachers, police officers and some public servants.