I think the most important thing we forget because we work at home is it is WORK.
We would never ever expect to be allowed to get up from our desks at a job away from home in an office setting, with the boss in the next room, to deal with an hour-long ordeal from our kids and their ups and downs. We would not be allowed to attend to family and friends calling us to chat at "the office" with the manager close by, so why do we allow ourselves to be pulled in at home? Because we can.
It is very hard but you have to remember that this has to work the right way for you or it is off to the office you go. The kids need to be reminded that too.
I feel quilty sometimes, especially in the summer when my 7-year-old asked me to come play outside at 10:30 in the moring. My father-in-law reminded me that I should not feel guily. If I was not able to be working at home she would be at a sitter's house I would be away for 8 or 9 hours a day. That made more sense than any reasons I had tried to convince myself of.
It is hard to tell the kids you are busy when they see you at the PC but I like the poster how said they lose something in the same amount of money that they caused you to lose,, might have to try that.