Oh dear! Are you sure your grandson did not know he was racking up bills?
Kids are very savvy these days, yes even 9 year olds!!
You should have put parental controls on and even asked his parents to use their cards instead of yours, I'm sure they're probably a lot more tech savvy than you are!
Everyone is saying not to blame the child, but surely he's partly responsible after Shinamae spoke to him prior to the debts occurring, and he would have then known not to click to get things until he knew if they were costing real money!!
I think he 'MAY' have thought, 'Meh! Granny won't find out until much later'!
Of course, I could be wrong, but please do not assume the child is totally innocent in this one, especially as they use computers all the time - paper is the thing to be doodled on these days, remember!!