In order to combat this, it is very helpful to have a dedicated space for working such as a table or desk. It is even better if this space can have its own room or office. By having a designated area, you can help to create a boundary for children to know that they need to stay away from those items.
Another thing that is useful for keeping children away from work items it to store what you need out of reach of the kids. This can be done with wall shelving, book shelves, or cabinets that can lock.
In addition to keeping kids out of your actual work area, many also find it to be difficult to keep kids out of your hair when you are actually working. I have found a few different ways to distract the kids when I really need to get something done right away. The first is to give them something to work on. This can be drawing a picture, reading a book, or writing a letter to gramma. I save movies and TV for the times when I have to be on the phone. This works great if you have a room with a TV just off of your working area. They can watch TV with volume, but it is still quiet enough so no one will know there are kids around.