I can give it a shot though just to see if the problem persists... for troubleshooting at least...
I'm not sure if you can change it permanently. Surely you can explore the options menu on the main menu to make it so.
If not, then the only other alternatives are that you change it manually every time, or perhaps learn the default function.
He's 9 - I tried to teach him about how regular flight controls would work, but he gets frustrated... I tried and I can persist the invert on the pad through reboots and power cycles, it never loses the setting for player 1, but player 2 it just refuses to remember at all...