Rabia,
My guys are 9 and 11. I started writing (with publication in mind...I began writing stories when I was 5!) when my oldest was about 5. Maybe earlier.
In the early days, I didn't plan on writing much while they were awake. If I absolutely, positively had to do an interview, I'd set them up with a toy they hadn't played with in a while. (But in case of emergencies, I had a cooler in my office with ice cream bars...if they stumbled in to my office, it kept 'em quiet, LOL.)
As they got older, I had a treasure box that was just for my interview/writing time. If I got, say, 20 minutes of quiet in, they got a prize from the box. I'm sure this reward system sets some people's teeth on edge, but it achieved what I needed it to and today my kids respect my writing time -- and they do things without need of constant rewards, too!
Nowadays, I use a cool salt lamp on my desk. If I absolutely don't want to be interrupted -- the muse is flowing or something -- I turn that light on. They know to wait until it's off to interrupt. The trick there is not to use it too often -- first of all, because as I said upthread, they're my first priority and second of all, it loses its oompf if I abuse it!
Kate