If one of your children ever scribble on their bedroom wall with a felt tip pen....First of all try the easiest way first which will be less harmful to your wall and then use more hardened methods if that doesn't work:
If the mark is still wet and or the wall is smooth and non-porous simply wipe with a dry paper towel with a little surgical spirit. Repeat this process again with a little more spirit if the mark is lifting.
Try paint remover basically as a last resort, being careful with it since it's flammable. Also note it may damage some wall finishes so test first on an unnoticeable area of the same surface.
Again if your child decides to write on his or her bedroom wall with a pencil....Relax...Simply grab a slice of fresh bread from the kitchen and rub the bread across the affected area. You should be able to remove the pencil marks without spoiling your wallpaper.