Give that it's generally a parent deciding that the child might take a flight without them it's also the parent who will be thinking about the potential risks and how to respond to them. So with regard to the molestation issue I think we've agreed it's almost certainly a fairly unlikely event, but concerning.
For some people the unlikelihood is enough to make them simply accept the risk and do nothing more.
Some may wish to change the odds and feel that insisting their child has no contact with men is the way to go about this. The feasibility of this is questionable, and given that the chances are already very low the utility of the response may be fairly small in any case. Some feel that this also creates a secondary risk to both society (men not wishing to interact with children even when they want to offer help to a child that requires it), to individual men and women impacted and also to the individual in question, by making them fearful of 50% of the populace, and possibly too trusting of the other 50%.
Others will feel the risk is too high and not allow their child to fly alone. Either a chaperone will be acquired (might be more risky of course, depending on the motivation of the chaperone), or the flight will not happen. There could be issues with that too.
Others may feel that there is little they can do to affect the risk that their child encounters someone who might behave badly toward them (in any way making their flight experience unpleasant, not just assaulting them) but that they can perhaps help their child develop some contingency plans, which might make the impact of the unpleasantness more manageable. Children who have been taught to be polite to strangers, respect their elders etc may find it very difficult to say no to unwanted advances or requests, so helping them to feel confident about their boundaries can really help. Plus this is a life skill not limited to plane journeys with few obvious downsides.