I suspect OP that this is a reason turned on its head for the modern generation, I bet back in the day children where put next to women as it would be concidered that men, shouldn't be bothered by children and the added bonus that a woman would "naturally" want to look after a child near them, so less work for cabin crew.
But I do agree with you, even with a 1/2500 chance, what are the odds that someone could abuse a child on a plane, too risky, abuser is as trapped as victim, to much risk of child talking, if child is put in isle seat theness risk they can move away easily.....
This is the most annoying of all sexism, as both sexes are being used by a business to keep costs down and minimal hassle to staff, way to go bastard big corp plc! Make your female passengers responsible for children you have been paid for and taken the money, male passengers out as peados because you think they won't do your job...most men actually do care about children, but why should they like the ladies and 2 you don't want a law suit based on their lack of safeguarding of passengers... Due to families not being seated together or taking children who should be cared for in loco patentis by the airline.
Fuck me! I am angry in so many shades of sexism and corporate bollocks!