So here's a very mommy post, we've been potty training and so I've had some fun ;) conversations with my daughter about the amount of toilet paper that you should use along with just how to use it. For anyone out there that would like to know how you're actually supposed to use toilet paper you can refer to this blog post from Cottenelle a year ago or read on.
Since kids use an average of 8 sheets for #1 and 16 for #2 this guideline is a good one for them to learn early on. For my little ones just learning I have them use only two sheets, their hands and bodies are small and any kid of potty training age can count to two at least so it makes it easy, then I show them how to fold it in half twice and then in half again the other direction so that you have a square. For #1 I have my girls wipe from front to back but for #2 I have my kids wipe from the back so that they won't wipe so far forward that they are wiping poop where it doesn't belong. It's a bit of a stretch but easy to reach the parts you actually need to get to. I teach them to wipe once and then check the paper and if there is poop on it then to get another two sheets and do it again until it comes back clean.
If they are making a mess wiping then it is often a sign that they aren't really done yet, there should be very little to wipe if they have actually gotten it all out and usually one or two wipes will do it.
This doesn't work with the cheap toilet paper, you usually have to use at least twice as much so keep that in mind.