Found this out quite by accident as my brother was doing some painting and remodeling in our bathroom. The bar that holds the toilet paper roll was covered in plaster dust and when I tried to spin it to get some toilet paper off of it, it did not spin nearly as easily as usual. Slowing down the spin would be a good thing in our house so not as much paper comes off with each pull. If you could somehow rough up the bar so it is not as smooth and made it a little harder to get it off the roll in the first place, I think it might greatly reduce your child's toilet paper usage.
I'm thinking that just flattening out the roll would have a similar effect, as it wouldn't spin as smoothly. What say you? Can the Parenthacker hive mind come up with an even better way to make toilet paper last longer?