Number One: If you need to have internet in your home, get KosherNet or some other filtering program, a serious one that is not so easy for the to get around.
Number Two: If you have a study in your home to do your work, and the kids don’t enter that room, then keep the computer there; if you don’t have a study, keep the computer in a public area of the house where every can see what you’re doing, and set rules that the children cannot log on without adult supervision.