@spikepipsqueak,
If your son has a login and password, I would completely uninstall the game, and then reinstall it. I might be wrong, but I think that with minecraft you buy an account rather than buying the game itself. If your son has a login and password, you shouldn't have to pay again. If your son doesn't have an account, then ignore what I am saying (I know how this works on my daughter's laptop, but I don't have an ipad).