Both of these things are really important parts of the whole "room of one's own" construct. It's not only the physical space, but the mental and temporal space, one craves. Not just freedom from interruptions, but freedom from the threat of interruptions, the possibility of distraction. So, for instance, even if Mr. B. is in charge of Pseudonymous Kid, hearing them argue over whether or not it's time for a bath is still a distraction. Or even, big picture, the fact of marriage and children at all: having a running tally in your head over whether you're out of milk and yogurt, whether your husband's been watching the kid for two hours or three and is it time for me to step in and give him a break yet, wondering if your partner remembered to call the bank or not. It's amazing, when you get a break from all that, to realize how much of a burden it is to carry around all the time, how much it imposes on your ability to think and write.
I recommend the comments, too.
I can't figure out how to do a permalink, so here's the next best thing--that article was posted on June 28, 2005.
Even though I have infinitely more slack about that sort of thing than most people, I'm still dealing with some of the issues.