Hi R. -
I recently started working from home myself. The first thing I did was talk with my kids. Tell them I was working, doing my job and when I was in my office, I was working. Not to inturupt while I was on the phone and no fighting (yeah right LOL).
It took a bit of reminders and holding the hand up when they just ran in the office while I was on the phone, but they started getting it when I ignored them. If I had to stop my call to deal with them, they had to go to their room and or lost a priviledge (if it was a repeat problem).
Soon they learned they enjoyed me being available and would come in quietly and wait, it took a few months, but being consistant really helps.
Now they love it, cause they get to do what they want while Im working, which can be a problem itself LOL. Though my kids are a little order (11 & 13) its been a year now and they have adjusted beautifully!
Make sure you set aside time during lunch for them, so they do get your undivided attention during the day. Make it a "special date" time and lots of attention. Snack time after school, take a break yourself, then give them free time so you can finish up. Try to make a schedule of sorts, even if its in 1 to 2 hr chunks with a 10 min break. Once a routine sets up, they will adjust (remember, they adjust to the school class routine very quickly!)
Best of luck.