OK... I'm probably not going to be very popular for this but...
I understand how you feel. I run my business from my home and need the computer/internet as well... I tend to get sucked into cyber-world myself, and because my kids (ages 6, 3, and 1) tend to play well for bursts of time by themselves it makes it even easier for me to be on the computer. To make it harder, I love those silly, addictive games on Facebook!
But I found that being on the computer is a choice. When I didn't make dinner one night and the kids came to me after playing outside and asked "where's dinner?" I had to pull my head out of my bahonkas. I had chosen to be on the computer instead of caring for my family and that was unacceptable to me. Now I am only on the computer 4 times a day, 5-6 a.m. and 10-11:15(ish) p.m. specifically for work, since the kids are sleeping and I can get more done, and then 2-15 minute bursts during the day, and these I have a timer to let me know when time is up. I can check my email on my phone, so I don't worry about customers emailing me during the day. So as other posters have said... make the choice and set limits on your computer time.
Also, if you say that being on the computer is a habit, then try something different. Instead of merely breaking the habit why don't you replace the bad habit with a better habit? (There's an old Latin proverb that says "habits are overcome by habits.") Instead of being on the computer, go and blow bubbles with your kids for 5 minutes or dust for a few minutes or even do 5 minutes of kickboxing (yeah, I love kickboxing!) It takes 30-45 days to break and create habits, so you'll have to keep at it. But just think to yourself, what is more important? My computer time or my family?
"Good habits, once established, are just as hard to break as are bad habits." - Robert Puller
Here's where I won't be so popular, 'cause I am not going to sugar-coat this...
Be the adult and make the choice. Set your priorities and stick with it.