You didn't fail. Wait for it. When they are out of the house on their own, go visit and use the bathroom. Bet the toilet paper roll is on and full. Guess where they learned it from? YOU! For sure they wouldn't dream of having their dispenser with only 4 squares available. And they fill it because your voice will resonate forever in their ears. Right now, they simply know it is your house and you are the boss and if you want the toilet paper dispenser filled, you can and will do it yourself. You didn't fail because you more than likely make sure there is some for them when they need it, don't you? If I see the toilet paper dispenser about a quarter of the roll gone, I set a new one on top of it. Someone eventually gets the hint...