The challenge is that the exchequer has no (expletive deleted) idea on how airlines collect their taxes for them.
Today the airline has no idea how old a passenger is simply from the booking record. If the kid was assessed the children's fare (only available on higher fares) then yes, they know the kid is under 12. But if the kid's fare is the same as any other passenger - the age information is not collected at booking - if ever.
The 'minister' is a hero for cancelling the tax, and his collectors (the airlines) are bums because they can't refund it.
If the Minister is running in your riding today, don't vote for him, he is an idiot.