I recently found a tip in Home Depot that I never would have put together myself. Granted I haven't used it yet so I can't say "yes, it works" or "no, it's useless". But I did buy some to try when there is a next time and I know there will be a next time...
Anyways, I read on a package of WD-40 that you can use it to remove crayon marks from walls.
Now, like I said I haven't tried this yet, and hey, this may even been common knowledge to everyone else in the world. Until this little girl of mine came along, it didn't cross my mind that a child would look at a wall and say "that's a good place for my crayon to go". LOL