For rips: It depends on the type of rip that happens to the book. If a page is torn you can just tape it with clear scotch tape. If the spine is broken you will want to use a stronger tape to hold the book together. In the situation of a broken spine, a duct style tape will work better. You may want to keep a few different types of tape around in case you come across a book with flaps that need to be reattached or pop up features that no longer pop.
For smudges or writing: It completely depends on the type of smudge or what was used when writing in the book. If your child wrote in a book with a pen, pencil (colored or uncolored), or a crayon you will want to go to an art supply store and get a rubber eraser. A rubber eraser is used by the artist to erase mistakes in paintings. It comes as a small white square. When you use it you roll it in your hand and gently blot it against the page. The marks should easily lift off onto the eraser. This will also work with nonsticky smudges. Please understand that this method might not clean the page entirely, but it will certainly help to clean the page up a bit. If your child has elected to use markers you are out of luck unless they are washable and you catch it the right way. If the markers are washable you may be able to use a small amount of water and a paper towel to blot the color out of the page.
In general: Work with your children to teach them how to properly treat halloween books for kids and put them away after each use. If you come across a repair that needs to be done and the answers are not here you can always check with your local library and see if they do book repairs. Many libraries offer this service to their patrons. You can also take a book into the library and ask their advice on how to best repair the book.