Ollie,
Woman can be pedophiles too, it is a psychological condition.
It is a condition of most airlines that crew supervise the UM throughout the flight, how can you be certain that by swapping male pax with a female that you haven't just made the situation into something that it wasn't? Both men and women are capable of heinous acts.
Should we also separate the elderly from dodgy looking fella in case they flog their purse. Or maybe separate those with a different religion in case of some uprising...
It comes down to the parent willing to accept that these are the risks associated with sending your child off on their own. The best way to deal with it - don't send them on their own.